Introduction
============

Mothers hold babies to their chest instinctively. Currently, in less well developed societies, where cribs, strollers, and infant seats are not common, mothers or other caregivers carry their infants on their chest for many hours a day.[@b1-phmt-6-015] Often there is nothing between the caregiver's chest and the baby's skin other than a diaper. This paradigm of holding an infant with ventral skin-to-skin contact (SSC), typically in an upright position and with the swaddled infant on the chest of the parent, is also commonly referred to as kangaroo care (KC), due to its simulation of marsupial care. While there are no recordings of infant care from the distant past, it is likely that KC of newborns has been practiced for eons. An example of the basic survival value of skin-to skin contact between infant and mother can be demonstrated when there is no interference from health care providers at delivery, specifically when the infant is placed skin-to-skin on its mothers chest at birth, within 20 minutes it will work its way toward the nipple and suckle.[@b2-phmt-6-015]

The medical use of this natural phenomenon was originally introduced by Edgar Rey Sanabria in Columbia in 1978 as a strategy to replace the function of incubators, which were in short supply in that country. Infants who were preterm, but otherwise stable, were put in continuous KC with their mothers. There are variations in KC practices, but all of it involves SSC. For example, kangaroo mother care (KMC) refers to SSC that is provided continuously until the infant begins to sweat and resist the position, an indication of more mature temperature regulation and development. Breastfeeding is exclusive, and discharge home occurs earlier than usual, when the baby is stable and the mother is comfortable providing continuous SSC.[@b3-phmt-6-015]--[@b5-phmt-6-015] Fathers and other family members can also be providers when the mother is unavailable.[@b6-phmt-6-015]

In resource-rich countries, SSC is seen as complementary to incubator care, and so continuous KC is rare. Implementation of SSC in hospitals has largely been motivated by a desire to humanize what has become a medical experience, and as partial fulfillment of the requirements set out in the Baby Friendly Hospital Initiative (BFHI).[@b7-phmt-6-015] The purpose of SSC in resource-rich countries has therefore been focused on facilitating infant transition to extrauterine life, promoting early bonding and establishing exclusive breastfeeding. SSC has shown added benefit for the mother, including reduced incidence of post-partum hemorrhage;[@b8-phmt-6-015] however, this review focuses primarily on the benefits to infants. More recently, strong evidence related to the pain-relieving benefits of SSC, almost exclusively studied in developed countries, has emerged.

KC has been studied for its effect on mortality, morbidity, physiological stability, breastfeeding, parental bonding, development, and pain control.[@b9-phmt-6-015]--[@b11-phmt-6-015] Yet despite consistent positive findings for all outcomes, adoption of KC as a routine clinical practice remains extremely variable across settings. It is recommended that KC is a feasible, natural, and cost-effective intervention, and should be standard of care in the delivery of quality health care for all infants, regardless of geographic location or economic status. What remains uncertain is whether continuous KC should be recommended in all settings or if there is a critical period of initiation, dose, or duration that is optimal. This review provides a synthesis of our current knowledge about the benefits of KC, highlighting differences and similarities across gestational age, low and higher resource countries, and in a non-pain and pain context. Additionally, implementation considerations and unanswered questions for future research are addressed.

Benefits of KC
==============

Since the inception of KC as a low-cost alternative to incubator care in areas with limited resources, clinicians and researchers have, over time, documented both physiologic and behavioral benefits for infant and mother (see [Table 1](#t1-phmt-6-015){ref-type="table"}). Many of these benefits have been researched sufficiently to permit meta-analysis, such that two Cochrane reviews exist on the subject.[@b9-phmt-6-015],[@b10-phmt-6-015] One focuses on healthy term or late-preterm newborns,[@b9-phmt-6-015] while the second includes low birth weight infants.[@b10-phmt-6-015]

Physiologic benefits
====================

Homeostasis (temperature regulation, physiological stability, blood glucose)
----------------------------------------------------------------------------

When compared with standard care (incubator, radiant warmer, or open crib), KC has shown benefits for homeostasis. Preterm infants who receive KC are more likely to maintain a healthy body temperature, and show increased cardiorespiratory stability.[@b10-phmt-6-015],[@b12-phmt-6-015]--[@b20-phmt-6-015] Looking at the entire hospitalization, KC is associated with decreased likelihood of infection, severe illness, and death.[@b10-phmt-6-015],[@b21-phmt-6-015] Additional evidence for the positive influence of KC exposure on autonomic regulation comes from a recent longitudinal study,[@b22-phmt-6-015] which showed a significant increase in baseline autonomic stability at 10 years follow-up. Even a very small amount of KC (1 hour a day for 14 days) provided to preterm infants compared with infants cared for only in an incubator was associated with improved infant and maternal outcomes. These findings are of particular interest because they are the first to demonstrate the long-lasting value of early KC.

Implications for practice
-------------------------

The evidence for the ability of KC to promote homeostasis is strong, especially in developing countries, where good evidence suggests that continuous KC can reduce mortality.[@b10-phmt-6-015] Unfortunately, the clinical picture is less clear in the developed world. The best evidence available is focused on intermittent use of KC, and while homeostatic benefits should theoretically persist when KC is continuous, there is a lack of studies designed to address this. Combined analysis conducted by Conde-Agudelo et al found that benefits that were clear in less developed countries (eg, reduction in sepsis, mortality, and severe illness) were not present when studies were limited to those in developed countries.[@b10-phmt-6-015] There remain limitations in making conclusions regarding the optimal time spent in KC to achieve maximum benefits. Feldman et al[@b22-phmt-6-015] offer compelling evidence that an average of 1 hour a day of KC may impart long-lasting benefits, but evidence is still lacking as to whether shorter or longer time periods may impart different benefits. Clinicians should use best judgment in balancing the illness acuity of individual infants, parent availability, and potential benefits.

Implications for research
-------------------------

Benefits that were discovered through research in developing countries should not be extrapolated to better resourced countries. There remains a paucity of studies investigating the effect of KC on mortality, infection, and serious illness in resource-rich countries. Methodologically rigorous studies are needed to understand how to maximize the clinical benefits of KC in hospital environments where advanced support is readily available. Many of the questions that remain are most appropriately answered by randomized controlled trials. In both developed and developing countries, our understanding of the physiological benefits of KC would benefit from routine use of composite physiological measures from which investigators can interpret a more meaningful clinical picture. In a review of the benefits of KC in term children, Moore suggests the use of SCRIP scores, (eg, stability of the cardiorespiratory system as the primary physiological outcome).[@b9-phmt-6-015] This would help draw conclusions that more broadly address stability as opposed to attempting to interpret outcomes separately.

There is little evidence from which to determine minimum times for KC to maximize physiological benefits, which are of particular interest to clinicians in countries like Canada and the United States of America (USA) where parent availability is often limited. Continuous KC potentially represents a free alternative to expensive equipment, but the price may be high for parents who bear the burden of additional costs associated with being available in neonatal intensive care units. A recent systematic review and meta-analysis[@b28-phmt-6-015] of 29 papers addressing parental experiences during KC, including 401 mothers and 94 fathers, revealed two overarching themes, ie, a beneficial and restoring effect on both themselves and their child(ren), but also an increased burden, which was a draining experience. Improving our understanding of the optimum daily duration of KC will be important in order to ensure that we do not unjustifiably transfer burden from the health care system to parents.

Late-preterm infants, primarily delivered in developed countries, who are deemed healthy enough to remain on the post partum ward, have been excluded from much of the current literature.[@b9-phmt-6-015] If physiological stability can be improved by introduction of early and sustained KC interventions for this population, there is potential for considerable impact on health care costs, family burden, and reduction of interventions. Similarly, there is a lack of analysis of benefits for infants born via cesarean section. In the studies included in this review, none considered analysis of outcomes in cesarean deliveries separately. This lack of evidence was one of the issues highlighted in a recent Cochrane review of vaginal versus cesarean birth for preterm infants.[@b29-phmt-6-015] While results of that meta-analysis found no difference in any of the reported outcomes (respiratory distress, Apgar scores, mechanical ventilation, supplemental oxygen), investigators were only able to include four trials, the most recent published in 1996.

For preterm or low birth weight infants, there is a need for more research examining the effectiveness of continuous early KC for both nonstabilized and relatively stabilized infants.[@b10-phmt-6-015] Perhaps unstable infants would benefit differentially from KC when compared with stable infants. Moreover, it remains unclear whether physiological benefits are variable depending on the KC provider, because there is so little research comparing mothers and alternative providers, such as fathers, grandparents, or trained volunteers.[@b22-phmt-6-015]

Growth, neurodevelopment, and neurosensory impairment
-----------------------------------------------------

Perhaps one of the most interesting benefits of KC is the effect on sleep, neurodevelopment, and growth. A recent study by Feldman et al[@b22-phmt-6-015] provides compelling evidence in this domain as well as in the physiological domain. They found that infants who received an average of 1 hour of KC for 14 days showed a more organized sleep--wake cycle at 10 years of age. Short-term benefits of KC on sleep patterns in preterm infants have been well established and include an increase in quiet sleep, longer cycles, and increased respiratory regularity.[@b15-phmt-6-015],[@b30-phmt-6-015],[@b31-phmt-6-015]

As a consequence of the tremendous rate of neurodevelopment that occurs in utero, it is no surprise that preterm infants often suffer neurophysiological sequelae.[@b32-phmt-6-015],[@b33-phmt-6-015] Two recent cohort studies used electroencephalographic complexity to measure differences in neurological maturity between preterm infants who received KC and those who did not. While sample sizes were small, the investigators were able to identify a relationship between KC and increased electroencephalographic complexity.[@b34-phmt-6-015] Additionally, the results showed an increase in primary motor cortex synchronization in response to transcranial magnetic stimulation in the group of infants that received KC.[@b35-phmt-6-015] These results suggest that KC plays a role in supporting neurodevelopment, which is consistent with earlier findings.[@b31-phmt-6-015]

A recent clinical trial in an Indian hospital compared sustained KC with conventional care in preterm infants. The infants were enrolled in groups of five, with the smallest three infants in each group being assigned to the KC condition.[@b36-phmt-6-015] Growth at a corrected gestational age of 40 weeks was similar between the intervention group and the control group, but infants receiving KC achieved more rapid physical growth after this point. Evidence for an association between KC and augmented growth comes from the meta-analysis by Conde-Agudelo et al, which found benefits for both continuous and intermittent KC.[@b10-phmt-6-015] When KC was continuous (KC) it was associated with an increase in weight gain, length, and head circumference.

Clinical implications
---------------------

Current evidence suggests that KC improves sleep, neurodevelopment, and growth, and should therefore be encouraged in clinical practice. While there is a lack of guidance regarding the optimal duration, the compelling outcomes described by Feldman et al were the result of just 14 days of sessions lasting an average of 1 hour.[@b20-phmt-6-015] Given the lack of uptake of any variation of KC in some practice settings, it would be reasonable to recommend that all infants should have KC initiated as soon as possible after birth and receive at least this minimal dose daily.

Research implications
---------------------

The potential for KC to impact neurodevelopment and growth in preterm infants is exciting, but there is still much left to be understood. Dose-response studies would be particularly interesting because they would help families and clinicians to collaborate in order to achieve the best outcomes for the least cost. Studies should be randomized when possible in order to help control for unknown confounding variables.

Investigators should take advantage of the diverse range of instruments available to them in order to learn more about the neurodevelopment changes associated with KC. For example, is the hypothesis that KC increases the rate of neurodevelopment supported by brain imaging? Are the benefits exclusive to pathways related to attention and sleep regulation, or do preterm infants who receive KC have more rapid peripheral neurodevelopment as well?

Studies designed to elucidate the mechanisms via which KC imparts its benefits are lacking. Sleep, neurodevelopment, weight, and length are clinically relevant outcomes but we also need studies designed to tease out how KC interacts with these.

Behavioral benefits
===================

Breastfeeding rates
-------------------

The BFHI, devised by the World Health Organization, is an international set of guidelines to promote, protect, and support breastfeeding.[@b7-phmt-6-015] Provision of KC is one of the "ten steps to successful breastfeeding" outlined in the BFHI. Although initially developed for healthy term infants, an international group of experts has made recommendations for adapting the "ten steps" of the BFHI to be applicable to ill and premature infants in neonatal settings.[@b37-phmt-6-015] In the modified BFHI for neonatal units proposed by Nyqvist et al,[@b37-phmt-6-015] provision of early, continuous, and prolonged KC without unjustified restrictions is cited as crucial to improving breastfeeding outcomes in this vulnerable infant population.

Evidence supports the influence of KC in increasing maternal milk volume and promoting breastfeeding exclusivity and duration in preterm infants.[@b38-phmt-6-015]--[@b40-phmt-6-015] Flacking et al[@b41-phmt-6-015] used a prospective longitudinal design to examine the influence of KC on breastfeeding in two age groups: those born very preterm (less than 32 weeks' gestational age) and preterm (32--36 weeks' gestational age). They found that in very preterm infants, those who were breastfeeding at 1, 2, 5, and 6 months post discharge has significantly more KC time in hospital. In randomized controlled trials comparing KC interventions with standard care, preterm infants demonstrate initiation of earlier breastfeeding,[@b10-phmt-6-015] higher breastfeeding exclusivity,[@b10-phmt-6-015],[@b42-phmt-6-015] and a longer duration of breastfeeding[@b10-phmt-6-015],[@b43-phmt-6-015],[@b44-phmt-6-015] when compared with infants who are cared for in an incubator or are wrapped in blankets when held by their mothers.

Clinical implications
---------------------

Based on consistent evidence for KC in promoting breastfeeding, clinicians should encourage KC for preterm infants both in the neonatal intensive care unit and following hospital discharge.[@b5-phmt-6-015],[@b6-phmt-6-015] Given the variability in duration of KC provided across studies, there is no consensus regarding the length of time required to optimize the benefit for breastfeeding outcomes. Therefore, it is recommended that mothers be informed of the benefits of KC for breastfeeding, and that they are encouraged and supported in providing KC as early as possible (ideally from birth) and for as long and as often as they would like.[@b31-phmt-6-015]

Limitations and implications for future research
------------------------------------------------

A limitation in the research examining KC and breastfeeding is the reliance on maternal self-report. Given the potential for bias in reporting breastfeeding outcomes due to the social desirability of exclusive breastfeeding, it is important to interpret the findings with caution. While some researchers[@b44-phmt-6-015] have considered and controlled for baseline maternal intentions to breastfeed, this is not consistently done. Given the significant influence of prenatal intentions to breastfeed in predicting long-term breastfeeding outcomes,[@b45-phmt-6-015] this is an important variable to measure and report in future studies. While Flacking et al[@b41-phmt-6-015] found that KC had the greatest benefit for very preterm infants (born at less than 32 weeks' gestational age), research in this young age group is limited. Future studies examining the relationship between KC and breastfeeding initiation, duration, and exclusivity in infants born at a gestational age of less than 32 weeks is needed. There was variability in measures of exclusivity of breastfeeding, length of KC intervention time in clinical trials, follow-up time points, and control interventions used (eg, incubator care, being wrapped in blankets when held) across the literature. Possibilities of both overestimation and underestimation of the effect of KC on breastfeeding stem from issues such as the treatment of breastfeeding as a dichotomous variable, failure to capture information such as nipple protractility, and "standard care" conditions that include breastfeeding counseling expertise which may not accurately reflect the day to day reality of the unit.[@b9-phmt-6-015] Consistency in interventions and outcomes is necessary to strengthen future research.

Parent--infant attachment
=========================

Attachment is defined as the emotional connection that is formed between infants and caregivers, and it is relevant for clinicians to consider this in infants of all gestational ages, especially in those born preterm.[@b46-phmt-6-015] Infant-maternal relationships have been shown to be less positive in infants born preterm, and evidence suggests that poor attachment can contribute to more negative outcomes.[@b46-phmt-6-015],[@b47-phmt-6-015]

Charpak et al[@b48-phmt-6-015] found that mothers in a KC group scored more favorably on sense of competence, feelings of worry or stress, sensitivity, and infant responsiveness. Total attachment scores determined through structured interviews by Gathwala et al[@b47-phmt-6-015] were higher in the KC group than in controls. An improved relationship with the infant was supported by higher scores in an investigation by Roberts et al,[@b49-phmt-6-015] and KC mother--infant pairs showed more symmetrical and less asymmetrical coregulation in a recent study that used the still-face paradigm tool as one of their outcomes.[@b50-phmt-6-015] Feldman et al[@b22-phmt-6-015] provided additional evidence supporting the relationship between KC and increased attachment behaviors across the post partum period in addition to greater mother--child reciprocity at 10 years. In one study excluded for using a crossover design, the investigators found no differences between KC and standard care at 4 or 12 months of age in measurement of infant interaction.[@b51-phmt-6-015]

Clinical implications
---------------------

A significant barrier to the provision of KC is the lack of facilities available for parents to stay (ie, sleep and cooking) near the infant to promote prolonged KC. This is a significant issue in both poorly resourced and resourced areas, although the trend toward single room versus open bay neonatal units and KC centers may lessen this concern and should be supported.[@b52-phmt-6-015]

Research implications
---------------------

A consistent approach to the measurement of parent--infant attachment would be of benefit because measures vary and make interpretation more difficult. The current evidence suggests that KC promotes greater parent--infant attachment, and the implications of this benefit should cause investigators to consider the inclusion of measures for attachment. Due to the potential neurodevelopment consequences of poor parent--infant attachment, increased information combined with longitudinal designs may help understand the basis of the seemingly neuroprotective effects of KC. More positive attachment may also partially explain some of the observed benefits to breastfeeding initiation and duration. There remains a knowledge gap with regard whether the same benefits in relationships that are observed between mother--infant dyads as a result of KC are also observed between father--infant[@b20-phmt-6-015] dyads.

KC in the context of pain
=========================

Given the benefits of improved physiological stability, and enhanced sleep and regulation, investigation of KC to diminish newborn procedural pain has become a rapidly growing field of study (see [Table 2](#t2-phmt-6-015){ref-type="table"}). The role of KC in this context was first examined in full-term infants in 2000 by Gray et al.[@b53-phmt-6-015] Three years later, Johnston et al examined its effectiveness in preterm infants at a gestational age of 32 to 36 weeks at birth.[@b54-phmt-6-015] Both studies reported a significant lowering of behavioral pain responses, and numerous other studies followed with similar results favoring KC. A recent Cochrane review included 19 randomized trials (n=1,594 infants, with 765 being term infants[@b54-phmt-6-015]--[@b67-phmt-6-015]) and used physiological, behavioral, and composite measures as the primary outcomes.[@b11-phmt-6-015] The majority of the studies[@b53-phmt-6-015]--[@b59-phmt-6-015],[@b64-phmt-6-015]--[@b70-phmt-6-015] (n=1,219) compared KC with standard care or no treatment, and used heel lance as the painful procedure.[@b53-phmt-6-015],[@b54-phmt-6-015],[@b56-phmt-6-015]--[@b67-phmt-6-015],[@b71-phmt-6-015]

Kangaroo care compared with incubator control
=============================================

Physiological parameters
------------------------

Physiological indicators reported were heart rate response, heart rate recovery, heart rate variability, oxygen saturation during the painful procedure, oxygen saturation after the painful procedure, and change in oxygen saturation. Twelve studies examined heart rate or heart rate variability during and/or heart rate recovery following a heel lance procedure.[@b53-phmt-6-015],[@b54-phmt-6-015],[@b56-phmt-6-015]--[@b58-phmt-6-015],[@b60-phmt-6-015],[@b64-phmt-6-015],[@b66-phmt-6-015],[@b67-phmt-6-015],[@b69-phmt-6-015]--[@b71-phmt-6-015] All studies favored KC or found no difference, but only a few studies could be combined in meta-analysis. Oxygen saturation during and/or following the painful procedure, reported by four studies,[@b64-phmt-6-015],[@b66-phmt-6-015],[@b69-phmt-6-015],[@b70-phmt-6-015] was unable to be combined. Although two of the studies[@b64-phmt-6-015],[@b70-phmt-6-015] reported that average oxygen saturation was higher in the KC group during the painful procedure, only Sajedi et al[@b70-phmt-6-015] showed these differences to be significant. Of two studies reporting change in oxygen saturation, neither found a difference between KC and standard care.[@b60-phmt-6-015],[@b67-phmt-6-015]

Validated pain assessment tools
-------------------------------

Validated pain scores, including the Premature Infant Pain Profile (PIPP),[@b54-phmt-6-015],[@b55-phmt-6-015],[@b59-phmt-6-015],[@b60-phmt-6-015],[@b64-phmt-6-015] Neonatal Facial Coding System,[@b56-phmt-6-015],[@b68-phmt-6-015] and Neonatal Infant Pain Scale[@b68-phmt-6-015]--[@b70-phmt-6-015] were measured in ten studies. Pain scores regardless of the tool used appeared to favor KC with lower Neonatal Facial Coding System scores during procedure, with a mean difference of 1.872 in favor of KC (*P*\<0.001) in Castral et al.[@b56-phmt-6-015] Both Sajedi et al[@b70-phmt-6-015] and Saeidi et al[@b69-phmt-6-015] reported Neonatal Infant Pain Scale scores that significantly favored KC. Five studies used the PIPP as the outcome for heel lance.[@b54-phmt-6-015],[@b55-phmt-6-015],[@b59-phmt-6-015],[@b60-phmt-6-015],[@b64-phmt-6-015] Based on the combined analysis of four studies,[@b54-phmt-6-015],[@b59-phmt-6-015],[@b60-phmt-6-015],[@b64-phmt-6-015] there was a significant effect post heel lance in favor of KC at 30 seconds, at 60 seconds,[@b54-phmt-6-015],[@b59-phmt-6-015],[@b64-phmt-6-015] and 90 seconds.[@b54-phmt-6-015],[@b59-phmt-6-015],[@b64-phmt-6-015] No significant difference between KC and controls were noted in PIPP scores at 120 seconds.[@b54-phmt-6-015],[@b59-phmt-6-015],[@b64-phmt-6-015] Additional outcomes, including endocrine response, cry duration, infant state, and adverse effects, were measured in a few small studies, with mixed or nonsignificant findings.[@b59-phmt-6-015]

Kangaroo care versus alternative treatments or alternative providers
====================================================================

Comparisons have been made in four studies with sweet taste,[@b60-phmt-6-015],[@b68-phmt-6-015] breastfeeding,[@b71-phmt-6-015] enhanced KC (including the addition of rocking and singing with KC),[@b62-phmt-6-015] fathers,[@b62-phmt-6-015] and unrelated females.[@b61-phmt-6-015] When KC with sweet taste (glucose) was compared with control in preterm neonates undergoing heel lance, heart rate, oxygen saturation variability, and PIPP scores all were reported to significantly favor KC. Similarly, heart rate, oxygen saturation, Neonatal Facial Coding System, and duration of crying were not reported to be different between KC and breastfeeding, but both were better than swaddled control.[@b60-phmt-6-015] The addition of auditory, vestibular, or gustatory factors with KC (rocking, singing, and offering the infant a finger or pacifier for sucking by the mother providing KC) did not result in any differences when compared with maternal KC alone. Two studies, both using a crossover design, compared the analgesic effect of maternal KC to SSC provided by an alternate caregiver: one with fathers[@b62-phmt-6-015] and the other with an unrelated woman.[@b61-phmt-6-015] In both cases, the differences in heart rate recovery and PIPP scores were not significant in spite of the large mean difference in favor of the mother, due mostly to high variance.

Clinical implications
---------------------

KC is a simple, natural, and cost-effective intervention to effectively diminish behavioral pain response in preterm infants. KC should be routinely offered to all infants undergoing needle-related procedures. Although there is some evidence that combining KC provided by the mother with sweet-tasting solutions may be synergistic, further study is warranted before this combination can be recommended as standard care. In the absence of a mother, a father,[@b62-phmt-6-015] unrelated woman,[@b61-phmt-6-015] or a co twin,[@b72-phmt-6-015],[@b73-phmt-6-015] may be considered as as there is some evidence that they may be an effective alternate.

Implications for research
-------------------------

Despite strong evidence that KC effectively lowers composite behavioral pain scores for both full-term and preterm infants as young as 28 weeks' gestational age undergoing a single heel lance or intramuscular injection compared with incubator control, there remain many unanswered questions. Studies examining the sustained effect of KC over repeated procedures, as well as studies with larger sample sizes replicating prior work, including similar outcomes, are required. Moreover, little is known about whether combining KC with other comforting interventions can enhance its benefits for pain relief. It is clinically important for future studies to examine the optimal dose or duration of KC needed to be effective. The range of time for KC prior to the painful procedure was 2 minutes[@b68-phmt-6-015] to 3 hours.[@b66-phmt-6-015] The only studies that compared times were two studies by Cong et al.[@b58-phmt-6-015],[@b59-phmt-6-015] Although both studies seemed to favor 30 minutes to either longer (80 minutes)[@b58-phmt-6-015] or shorter doses (15 minutes),[@b59-phmt-6-015] other studies using different outcomes favored KC for times longer and shorter than 30 minutes, so no conclusion can be made. Investigators should consider reporting findings from the entire sample as well as differentiating among gestational ages when possible. Lastly, examining whether the benefits of KC associated with early pain reduction and immediate pain relief may also lead to improved longer term outcomes are needed.

Considerations for implementation
=================================

In spite of the plethora of documented benefits of KC in preterm infants, KC is not consistently practiced in this population. In a national survey of nurse managers in USA Newborn Intensive Care Units (NICUs), Engler et al[@b74-phmt-6-015] found that while 82% of respondents indicated that KC was implemented in some form on their unit, practice was informed by nurse perceptions as opposed to scientific evidence. It has been consistently demonstrated that both parents and clinicians perceive KC as a positive intervention for mothers and their infants.[@b75-phmt-6-015]--[@b79-phmt-6-015] However, despite generally positive attitudes, inconsistencies may exist in parent and nurse perceptions of optimal KC practices. For example, in a recent prospective cohort study conducted by Hendricks-Munoz et al,[@b80-phmt-6-015] parents and nurses both reported that KC benefits infants; however, only 18% of nurses compared with 63% of mothers believed that KC should be provided to their infants on a daily basis.

In addition to varying attitudes toward KC, numerous barriers have been identified. A consistently described barrier relates to the safety of facilitating KC in the preterm infant. Specifically, the highly technological equipment used to care for these infants has been identified as limiting opportunities for KC,[@b74-phmt-6-015],[@b76-phmt-6-015]--[@b79-phmt-6-015],[@b81-phmt-6-015],[@b82-phmt-6-015] with several studies reporting inconsistent policies and KC practices in infants who are intubated or have arterial or venous lines in place.[@b74-phmt-6-015],[@b81-phmt-6-015] Maternal concern around infant well-being during KC, such as fear that the infant may stop breathing, is another concern that has been reported.[@b77-phmt-6-015],[@b79-phmt-6-015] Inadequate staff education and experience in facilitating KC for clinically compromised infants was another barrier identified, as well as lack of staff and time to appropriately support KC in both the NICU[@b74-phmt-6-015],[@b77-phmt-6-015],[@b79-phmt-6-015],[@b81-phmt-6-015] and following delivery by cesarean section.[@b83-phmt-6-015] Both parents and health care providers identified the NICU environment as limiting parental visitation and opportunities to provide KC. For example, frequently identified barriers included lack of privacy, space, and comfortable chairs at the bedside, as well as a lack of facilities for meal preparation and parental rooming in.[@b77-phmt-6-015],[@b78-phmt-6-015],[@b81-phmt-6-015],[@b84-phmt-6-015] Parent-related factors such as maternal pain (eg, breast, back, or incisional pain),[@b77-phmt-6-015],[@b85-phmt-6-015] having responsibilities in the home (eg, other children, chores),[@b77-phmt-6-015],[@b81-phmt-6-015],[@b85-phmt-6-015] and limited knowledge of the benefits of KC were additional barriers that were identified to limit the availability and motivation of mothers to provide KC.[@b81-phmt-6-015]

While it is evident that there are numerous barriers to successful implementation of KC, findings also highlight ways in which to facilitate this practice in preterm infants. Educational interventions have been consistently cited as necessary to train staff in the knowledge and skills needed to promote and support KC effectively.[@b74-phmt-6-015],[@b76-phmt-6-015],[@b80-phmt-6-015],[@b81-phmt-6-015],[@b86-phmt-6-015] In a recent prospective cohort study examining the impact of a training program on KC perceptions and practice competency, nurses received didactic education and simulation training for assessing and placing infants in KC.[@b80-phmt-6-015] Nurses' competency in supporting KC for infants requiring nasal continuous positive airway pressure and mechanical ventilation improved from 30% to 92% (*P*\<0.001) and from 10% to 48% (*P*\<0.004), respectively. In addition, nurses who reported feeling uncomfortable in this competency decreased to 0%, and the perceived value increased from 50% to 100% (*P*\<0.001). Having clear policies in place to guide evidence-informed KC implementation,[@b74-phmt-6-015],[@b81-phmt-6-015],[@b86-phmt-6-015] as well as KC leaders and unit-based champions,[@b81-phmt-6-015] have also been identified as ways to facilitate ease of use in ill full-term and preterm infants.

In addition to educational interventions for staff, parent education regarding the benefits of KC and how to safely hold their infant in addition to assessing their well-behind has been documented as a way to encourage KC implementation.[@b78-phmt-6-015],[@b81-phmt-6-015],[@b83-phmt-6-015],[@b86-phmt-6-015],[@b87-phmt-6-015] Modification of the physical environment by providing privacy screens, comfortable chairs, and family rooms has been identified by parents to support KC.[@b77-phmt-6-015],[@b78-phmt-6-015] Finally, assistance in positioning infants in KC, providing parents with information and practical advice, as well as providing reminders and follow-ups around KC practices,[@b77-phmt-6-015],[@b78-phmt-6-015],[@b81-phmt-6-015],[@b87-phmt-6-015] have been identified by both parents and health care providers as valuable in supporting the implementation of KC.

Conclusion
==========

Kangaroo care is a natural, effective, and low-cost intervention that can be utilized in any setting. There is strong evidence related to its numerous benefits, including physiological, behavioral, and pain-relieving aspects for preterm newborns, both healthy and ill, as well as less stress and improved self-efficacy in parents. Mothers and family members have a unique relationship and are highly invested to ensure that optimal outcomes are achieved for their newborns. Yet their active participation in care often remains underutilized. Despite a few remaining unanswered questions, the use of KC should be considered standard of care for all infants and be initiated early with the ultimate goal to minimize separation of the mother--infant dyad.

More evidence is required in order to recommend implementation of KC in resource-rich environments. Though it is tempting to make this recommendation considering the diverse array of benefits offered, questions remain as to how implementation might affect mortality, infection, and severe illness. There a need for dose-response studies in this population that include a continuous or near-continuous arm, but these should be accompanied by economic measurements that will determine the tangible and intangible costs taken on by parents. To this end, health economists should be considered as potential members of the interdisciplinary team. Additionally, in poorly resourced countries, greater government funding should target the creation of KC centers that incorporate clean water, cooking, and sleeping facilities for mothers to remain exclusively with their infants.

**Disclosure**

The authors report no conflicts of interest in this work.

###### 

Benefits of KC in non-pain context

  -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Reference                                                 Sample and setting                                                              Design                                                                                   Provider                                                                Outcome measures                                                                                                    Results
  --------------------------------------------------------- ------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------- ----------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  **Temperature regulation**                                                                                                                                                                                                                                                                                                                                                                                                     

  Christensson et al[@b12-phmt-6-015]                       Sample: n=80, \>1,500 g\                                                        RCT: KC versus incubator for treatment of hypothermia                                    Mother                                                                  Rectal temperature                                                                                                  KC \> control normal temperature at 240 minutes (90% versus 60%, *P*\<0.001)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: teaching hospital, Zambia                                                                                                                                                                                                                                                                                                                                   

  Conde-Agudelo et al[@b10-phmt-6-015]                      Sample: n=698\                                                                  Meta-analysis of RCTs                                                                    Mother                                                                  Hypothermia at discharge or 40--41 weeks of PMA                                                                     KC \< SC (RR 0.34, 95% CI 0.17--0.67)
                                                            LBW infants (six studies)                                                                                                                                                                                                                                                                                                                                            

  Ludington-Hoe et al[@b13-phmt-6-015]                      Sample: n=29, preterm (26--35 weeks)\                                           RCT: KC ×3\                                                                              Mother                                                                  Abdominal and toe temperature                                                                                       Abdominal temperature: no difference\
                                                            Mode of delivery: not reported\                                                 2.5--3.0 hours versus SC                                                                                                                                                                                                                                                             Toe temperature: KC \> SC (*F*=7.04, *P*=0.02)
                                                            Setting: level II NICU in USA                                                                                                                                                                                                                                                                                                                                        

  Legault and Goulet[@b14-phmt-6-015]                       Sample: n=61, premature (32--35 weeks)\                                         Randomized crossover trial                                                               Mother                                                                  Skin temperature                                                                                                    No difference
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: level III NICU, Canada                                                                                                                                                                                                                                                                                                                                      

  Chwo et al[@b15-phmt-6-015]                               Sample: n=34, 34--36 weeks GA\                                                  RCT: KC versus control versus SC                                                         Mother                                                                  Tympanic temperature                                                                                                KC \> SC (MD 37.3°C versus 37.0°C, *P*=0.01)
                                                            Mode of delivery: V (n=11) C/S (n=23)\                                                                                                                                                                                                                                                                                                                               
                                                            Setting: Taiwan                                                                                                                                                                                                                                                                                                                                                      

  Marin Gabriel et al[@b16-phmt-6-015]                      Sample: n=137, 35--42 weeks GA\                                                 RCT: early KC ×2 hours versus SC                                                         Mother, early KC ×2 hours                                               Axillary temperature                                                                                                Rise in temperature first 5 minutes: KC \> SC 0.07°C±0.58°C versus −0.22°C±0.52°C in the CG (*P*\<0.001).\
                                                            Mode of delivery: V\                                                                                                                                                                                                                                                                                                                                                 Mean temperature first 5 minutes of life: 36.6°C±0.79°C in the KC group versus 36.9°C±0.58°C in the CG (*P*\<0.01)
                                                            Setting: hospital, Spain                                                                                                                                                                                                                                                                                                                                             

  Gathwala et al[@b43-phmt-6-015]                           Sample: n=110 LBW infants (35 weeks mean GA)\                                   RCT: KC at least 6 hours/day versus incubator care; 16-month longitudinal study          Mother                                                                  Mean axillary temperature, episodes of hypothermia                                                                  Mean temperature: KC \> SC (36.67°C±0.24°C versus 36.44°C±0.22°C; *P*\<0.05)\
                                                            Mode of delivery: not reported                                                                                                                                                                                                                                                                                                                                       Episodes of hypothermia: no statistically significant difference

  **Physiological stability**                                                                                                                                                                                                                                                                                                                                                                                                    

  Bergman et al[@b17-phmt-6-015]                            Sample: 31 KC, mean 34.2 weeks; 13 controls, mean 35.3 weeks\                   31 KC, mean 34.2 weeks; 13 controls, mean 35.3 weeks                                     Mother                                                                  SCRIP[a](#tfn1-phmt-6-015){ref-type="table-fn"} score during first 6 hours after birth\                             Higher scores in KC (MD 2.88; 95% CI 0.53--5.23).\
                                                            Mode of delivery: V\                                                                                                                                                                                                                             Infants who did not exceed defined physiological parameters requiring attention                                     Attention more likely to be required in SC group (RR 10.83; 95% CI 1.63--72.02)
                                                            Setting: two secondary hospitals in South Africa                                                                                                                                                                                                                                                                                                                     

  Ludington-Hoe et al[@b18-phmt-6-015]                      Sample: 24 preterm (33--35 weeks GA at birth)\                                  RCT: KC versus SC in infants nearing discharge                                           Mother                                                                  HR, RR, O~2~ saturation, abdominal skin temperature                                                                 Mean cardiorespiratory and temperature outcomes within acceptable ranges during KC; no apnea, bradycardia, or periodic breathing in KC; KC \> regular breathing
                                                            Mode of delivery: N/A\                                                                                                                                                                                                                                                                                                                                               
                                                            Setting: NICU, USA                                                                                                                                                                                                                                                                                                                                                   

  Mitchell et al[@b19-phmt-6-015]                           Sample: n=38, 27--30 weeks GA\                                                  RCT: 2 hours KC versus SC                                                                Mother                                                                  HR, O~2~ saturation                                                                                                 Bradycardia/hour: KC \< SC (*P*=0.048) O~2~ desaturation events: KC \< SC (*P*=0.017)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: NICU, USA                                                                                                                                                                                                                                                                                                                                                   

  Legault and Goulet[@b14-phmt-6-015]                       Sample: n=61, premature (32--35 weeks)\                                         RCT crossover                                                                            Mother                                                                  HR, RR, O~2~ saturation                                                                                             O~2~ saturation: KC \> SC (92.8% versus 90.5%, *P*\<0.0001)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: level III NICU, Montreal, Canada                                                                                                                                                                                                                                                                                                                            

  Rojas et al[@b20-phmt-6-015]                              Sample: 60 LBW (32 weeks, \<1,500 g)\                                           RCT: KC for 1 hour versus holding clothed in supine position                             Mothers and fathers (70±40 minutes/day)                                 Percentage of infants with O~2~ desaturation during observation                                                     KC \< control (30% versus 56%, *P*=0.05)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: pediatric hospital, USA                                                                                                                                                                                                                                                                                                                                     

  **Sleep organization**                                                                                                                                                                                                                                                                                                                                                                                                         

  Ludington-Hoe et al[@b30-phmt-6-015]                      Sample: n=28, PMA 32 weeks\                                                     RCT: 2--3 hours KC versus SC                                                             Mother                                                                  Sleep arousal, REM, quiet sleep, indeterminate sleep                                                                Sleep arousal: KC \< SC (BKC = −7.35, *P*=0.015);\
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      REM counts during AS: KC \< SC REM counts during AS (BKC = −8.9, *P*=0.029)\
                                                            Setting: USA                                                                                                                                                                                                                                                                                                                                                         REM counts during study period: KC \< SC (BKC = −5.11, *P*=0.013)\
                                                                                                                                                                                                                                                                                                                                                                                                                                 Quiet sleep: KC \> SC % QS (β = +10.3, *P*=0.05),\
                                                                                                                                                                                                                                                                                                                                                                                                                                 Indeterminate sleep: KC \< SC % IS (β = −9.0, *P*=0.01)

  Chwo et al[@b15-phmt-6-015]                               Sample: n=34, 34--36 weeks GA\                                                  RCT: KC versus control versus SC                                                         Mother, 3 hours                                                         Quiet sleep (recorded at 5-minute intervals)                                                                        KC \> control (62% versus 22%, *P*=0.001)
                                                            Mode of delivery: V (n=11) C/S (n=23)\                                                                                                                                                                                                                                                                                                                               
                                                            Setting: Taiwan                                                                                                                                                                                                                                                                                                                                                      

  Scher et al[@b31-phmt-6-015]                              Sample: eight preterm\                                                          Cohort comparison                                                                        Mother                                                                  Sleep analysis (EEG)                                                                                                REM counts during study period: KC \< SC (*P*\<0.0001) Sleep cycle length: KC \> control (*P*=0.01)\
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      Quiet sleep: KC \> control (*P*=0.0001) Spectral beta power: KC \< control (*P*=0.025) Spectral respiratory irregularity: KC \> control (*P*=0.02)
                                                            Setting: USA                                                                                                                                                                                                                                                                                                                                                         

  **Mortality**                                                                                                                                                                                                                                                                                                                                                                                                                  

  Conde-Agudelo et al[@b10-phmt-6-015]                      Sample: 1,736 LBW infants (eight studies)\                                      Meta-analysis of RCTs                                                                                                                                            Mortality at discharge or 40--41 weeks PMA\                                                                         KC \< SC (RR 0.60; 95% CI 0.39--0.92)\
                                                            2,167 LBW infants (eleven studies)                                                                                                                                                                                                               Mortality at latest follow-up                                                                                       KC \< SC (RR 0.67; 95% CI 0.48--0.95)

  **Infection**                                                                                                                                                                                                                                                                                                                                                                                                                  

  Conde-Agudelo et al[@b10-phmt-6-015]                      Sample: 1,343 stabilized LBW infants (seven studies)                            Meta-analysis of RCTs                                                                    Mother                                                                  Severe infection/sepsis at latest follow-up                                                                         KC \< SC (RR 0.56; 95% CI 0.40--0.78)

  283 LBW (one study)                                                                                                                                                                                                                Severe illness at 6 months                                              KC \< SC (RR 0.30; 95% CI 0.14--0.67)                                                                               

  913 LBW (three trials)                                                                                                                                                                                                             Nosocomial infection/sepsis at discharge or 41 weeks PMA                KC \< SC (RR 0.45; 95% CI 0.27--0.76)                                                                               

  283 LBW (one study)                                                                                                                                                                                                                Lower respiratory tract disease at 6 months follow-up                   KC \< SC (RR 0.89; 95% CI 0.15--0.89)                                                                               

  1,266 LBW infants (four studies)                                                                                                                                                                                                   Mild/moderate infection or illness at latest follow-up                  No difference (RR 1.28; 95% CI 0.87--1.88)                                                                          

  448 LBW (four studies)                                    RCT                                                                             Mother                                                                                   Hyperthermia at discharge or 40--41 weeks' PMA                          No difference (RR 0.79; 95% CI 0.59--1.05)                                                                          

  Sloan et al[@b21-phmt-6-015]                              Sample: 283 LBW (mean GA 33 weeks)\                                             RCT: KC w/frequent BF versus SC with scheduled BF                                        Mother                                                                  Diarrhea at 6 months follow-up                                                                                      No difference (RR 0.65; 95% CI 0.35--1.20)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: Ecuador                                                                                                                                                                                                                                                                                                                                                     

  **Growth**                                                                                                                                                                                                                                                                                                                                                                                                                     

  Conde-Agudelo et al[@b10-phmt-6-015]                      1,072 LBW (ten studies)                                                         Meta-analysis of RCTs                                                                    Mother                                                                  Weight/day                                                                                                          KC \> control (MD 3.7 g, 95% CI 1.9--5.6)

  251 LBW (two studies)                                                                                                                                                                                                              Length (cm)                                                             KC \> control (MD 0.29 cm, 95% CI 0.27--0.31)                                                                       

  369 LBW (three studies)                                                                                                                                                                                                            Head circumference                                                      KC \> control (MD 0.18 cm, 95% CI 0.09--0.27)                                                                       

  Charpak et al[@b48-phmt-6-015]                            592 LBW                                                                         RCT: 24 hours/day KC versus SC                                                           Mother                                                                  Head circumference at 6 months' corrected age                                                                       KC \> control (MD 0.34 cm, 95% CI 0.11--0.57)

  Nagai et al[@b27-phmt-6-015]                              Sample: 73 LBW 32--34 weeks GA\                                                 RCT, early (\<24 hours) versus late (\>24 hours) onset KC in relatively stable infants   Mother                                                                  Reduction in body weight loss from birth to 48 hours                                                                KC \> control (MD 43.4 g, 95% CI 5.5--81.1)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: five hospitals, Iran                                                                                                                                                                                                                                                                                                                                        

  Rojas et al[@b20-phmt-6-015]                              Sample: 60 LBW (≤32 weeks, \<1,500 g)\                                          RCT: KC for 1 hour versus holding clothed in supine                                      Mothers and fathers (70±40 minutes/day)                                 Rate of head growth                                                                                                 Total head growth: KC \> control (*P*=0.03)\
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      Head growth rate: KC \> control (*P*=0.05)
                                                            Setting: pediatric Hospital, USA                                                                                                                                                                                                                                                                                                                                     

  Suman et al[@b23-phmt-6-015]                              Sample: 206 \<2,000 g\                                                          RCT                                                                                      Mothers, 13.5 hours/day average                                         Growth                                                                                                              KC \> control (weight 2,388 g, length 47.8 cm, and head circumference 33.4 cm versus weight 2,065 g, length 46.4 cm, and head circumference 32.1 cm; *P*\<0.05)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: level III NICU in Western India                                                                                                                                                                                                                                                                                                                             

  Gathwala et al[@b43-phmt-6-015]                           Sample: 110 LBW infants (35 weeks mean GA)\                                     RCT KC at least 6 hours/day versus incubator care.\                                      Mother                                                                  Weight gain, length, head circumference                                                                             Weight: KC \> SC (16.23±0.49 g/day versus 14.10±0.52 g/day; *P*\<0.05)\
                                                            Mode of delivery: not reported Setting: hospital, India                         16-month longitudinal study                                                                                                                                                                                                                                                          Length: KC \> SC (1.03±0.05 cm/week versus 0.74±0.05 cm/week; *P*\<0.05)\
                                                                                                                                                                                                                                                                                                                                                                                                                                 Head circumference: KC \> SC (0.59±0.04 cm/week versus 0.47±0.03 cm/week, *P*\<0.05)

  **NICU admissions/hospital length of stay/readmission**                                                                                                                                                                                                                                                                                                                                                                        

  Bergman et al[@b17-phmt-6-015]                            Sample: 31 KC, mean 34.2 weeks; 13 controls, mean 35.3 weeks\                   RCT: KC in first 6 hours post birth versus SC                                            Mother                                                                  NICU admission                                                                                                      No difference (RR 1.44; 95% CI 0.15--14.29)
                                                            Mode of delivery: V\                                                                                                                                                                                                                                                                                                                                                 
                                                            Setting: two secondary hospitals in South Africa                                                                                                                                                                                                                                                                                                                     

  Conde-Agudelo et al[@b10-phmt-6-015]                      946 LBW (two studies)\                                                          Meta-analysis of RCTs                                                                    Mother                                                                  Readmission to hospital at latest follow-up\                                                                        No difference (RR 0.60; 95% CI 0.34--1.06)\
                                                            931 LBW (ten studies)                                                                                                                                                                                                                            Length of hospital stay (days)                                                                                      KC \< SC (MD −2.17, 95% CI −3.72, −0.63)

  Nagai et al[@b27-phmt-6-015]                              Sample: 73 LBW 32--34 weeks GA\                                                 RCT: early (\<24 hours) versus late (\>24 hours) onset KC in relatively stable infants   Mother                                                                  Length of hospital stay (days)                                                                                      Non-significant difference, early KC \< late KC (MD --0.9, 95% CI −3.01 to 1.2)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: five hospitals, Iran                                                                                                                                                                                                                                                                                                                                        

  **Breastfeeding rates/milk volume**                                                                                                                                                                                                                                                                                                                                                                                            

  Conde-Agudelo et al[@b10-phmt-6-015]                      1,333 LBW (five studies)\                                                       Meta-analysis of RCTs                                                                    Mother                                                                  EBF at discharge or\                                                                                                KC \> control (RR 1.20; 95% CI 1.07--1.34)\
                                                            600, LBW (five studies)\                                                                                                                                                                                                                         40--41 weeks PMA\                                                                                                   KC \> control (RR 1.20; 95% CI 1.01--1.43)\
                                                            1,576 LBW (nine studies)\                                                                                                                                                                                                                        EBF at 1 month follow-up\                                                                                           KC \> control (RR 1.20; 95% CI 1.06--1.36)\
                                                            538 LBW (six studies)\                                                                                                                                                                                                                           Any BF at discharge or 40--41 weeks PMA\                                                                            KC \> control (RR 1.33; 95% CI 1.00--1.78)\
                                                            924 LBW (five studies)                                                                                                                                                                                                                           Any BF at 1--2 months follow-up\                                                                                    KC \> control (RR 1.14; 95% CI 1.06--1.23)
                                                                                                                                                                                                                                                                                                             Any BF at 3 months follow-up                                                                                        

  Svensson et al[@b24-phmt-6-015]                           Sample: 103, 1--16 weeks post-partum with difficulty with latching\             RCT: KC versus fully clothed                                                             Mother                                                                  Maternal experience, time to latch                                                                                  Time to regular latching: KC \< control (2.0 weeks, Q1 =1.0, Q3 =3.7 versus 4.7 weeks Q1 =2.0, Q3 =8.0, *P*=0.020); 94% of infants in KC with hx of "strong reaction" during "hands-on latch intervention" latched within 3 weeks versus 33% of control (*P*=0.0001)\
                                                            Mode of delivery: V (n=67), C/S (n=36)\                                                                                                                                                                                                                                                                                                                              Mothers' positive feelings: KC \> control, *P*=0.022
                                                            Setting: university hospital, Sweden                                                                                                                                                                                                                                                                                                                                 

  Chiu and Anderson[@b25-phmt-6-015]                        Sample: 100 dyads, 32--37 weeks GA\                                             RCT: early KC (mean 1.3 hours ×11.6 times) versus SC                                     Mother                                                                  Nursing Child Assessment Satellite Feeding Scale and Teaching Scale                                                 Infant teaching scores: KC \< SC at 6 months (*P*=0.001), SC \> child's response to caregiver subscale (*P*=0.001)
                                                            Mode of delivery: V (n=73), C/S (27)\                                                                                                                                                                                                                                                                                                                                
                                                            Setting: university Hospital, USA                                                                                                                                                                                                                                                                                                                                    

  Rojas et al[@b20-phmt-6-015]                              Sample: 60 LBW (≤32 weeks, \<1,500 g)\                                          RCT: KC for 1 hour versus holding clothed in supine                                      Mothers and\                                                            Successful BF                                                                                                       KC \> control (OR 10, 95% CI 8--57, *P*=0.01)
                                                            Mode of delivery: not reported\                                                                                                                                          fathers (70±40 minutes/day)                                                                                                                                                                 
                                                            Setting: pediatric hospital, USA                                                                                                                                                                                                                                                                                                                                     

  Hake-Brooks and Anderson[@b44-phmt-6-015]                 Sample: 66 preterm infants 32--36 weeks\                                        RCT                                                                                      Mothers (4.47 hours)                                                    Breastfeeding status at hospital discharge and at 1.5, 3, 6, 12, and 18 months as measured by Breastfeeding Index   Breastfeeding duration: KC \> control (5.08 months versus 2.05 months, *P*=0.003)\
                                                            Mode of delivery: N/A in\                                                                                                                                                                                                                                                                                                                                            Breastfeeding exclusivity: KC \> control *P*=0.047\
                                                            Setting: hospital, USA                                                                                                                                                                                                                                                                                                                                               Full exclusivity: KC \> control at discharge, 1, 5, 3, and 6 months

  Gathwala et al[@b43-phmt-6-015]                           Sample: 110 LBW infants (35 weeks mean GA)\                                     RCT, KC (at least 6 hours/day) versus incubator care. 16-month follow-up.                Mother                                                                  Breastfeeding status                                                                                                Exclusive BF initiated with all infants; at study conclusion (16 months): KC \> SC (44/50 versus 36/50; *P*\<0.05)
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: hospital, India                                                                                                                                                                                                                                                                                                                                             

  Heidarzadeh et al[@b42-phmt-6-015]                        Sample: 251 premature (\>27 weeks)\                                             Cross-sectional                                                                          Mothers and fathers                                                     Exclusive breastfeeding at time of discharge                                                                        KC \> SC (OR: 4.1; 95% CI: 2.2--7.5
                                                            Mode of delivery: V (n=86), C/S (n=165)\                                                                                                                                                                                                                                                                                                                             
                                                            Setting: hospital, Iran                                                                                                                                                                                                                                                                                                                                              

  Hurst et al[@b40-phmt-6-015]                              Sample: 24 LBW infants\                                                         Retrospective comparison following policy initiation of KC                               Mother                                                                  24-hour milk volume                                                                                                 KC \> control (strong linear increase, versus no change)
                                                            Mode of delivery: NA\                                                                                                                                                                                                                                                                                                                                                
                                                            Setting: N/A                                                                                                                                                                                                                                                                                                                                                         

  **Time crying**                                                                                                                                                                                                                                                                                                                                                                                                                

  Chwo et al[@b15-phmt-6-015]                               Sample: n=34, 34, 36 weeks GA\                                                  RCT: KC versus control versus SC                                                         Mother, KC 3 hours ×2 days                                              Number of times observed crying during 3-hour period                                                                KC \< control (2% versus 6%, *P*=0.001)
                                                            Mode of delivery: V (n=11) C/S (n=23)\                                                                                                                                                                                                                                                                                                                               
                                                            Setting: Taiwan                                                                                                                                                                                                                                                                                                                                                      

  **Neurodevelopment**                                                                                                                                                                                                                                                                                                                                                                                                           

  Charpak et al[@b48-phmt-6-015]                            Sample: 588 LBW\                                                                RCT (all outcomes at 12 months corrected age)                                            Mother                                                                  Psychomotor development, cerebral palsy, deafness, visual impairment                                                Psychomotor development: no difference\
                                                            Mode of delivery: V, C/S\                                                                                                                                                                                                                                                                                                                                            Cerebral palsy: no difference (RR 0.65; 95% CI 0.21--2.02) Deafness: no difference (RR 0.30; 95% CI 0.03--2.90)\
                                                            Setting: tertiary center, Colombia                                                                                                                                                                                                                                                                                                                                   Visual impairment: no difference (RR 0.91; 95% CI 0.53--1.56)

                                                            Sample: 579 LBW                                                                                                                                                                                                                                  General developmental quotient                                                                                      KC \> control (*P*\<0.01)

  Schneider et al[@b35-phmt-6-015]                          Sample: 39 adolescent former premature (\<33 weeks GA) and nine born at term\   Longitudinal follow-up of RCT                                                            Mothers/fathers/family (24 hours/day)                                   Motor systems maturation via transcranial magnetic stimulation                                                      MEP latency: KC \< control (*P*=0.03); in KC, decrease in MEP latency correlated with time in KC (*P*=0.02)\
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      Short-interval intracortical inhibition and facilitation in M1: no difference, but obtained more easily in KC and term groups\
                                                            Setting: Bogotá, Colombia                                                                                                                                                                                                                                                                                                                                            Interhemispheric inhibition: more frequent, with shorter latency and longer duration in KC (*P*\<0.0001)\
                                                                                                                                                                                                                                                                                                                                                                                                                                 Group × sex × side interaction: shorter latency in all KC and term subjects in dominant (*P*≤0.0001) and non-dominant (*P*≤0.001) hemispheres\
                                                                                                                                                                                                                                                                                                                                                                                                                                 No differences between KC and term

  **Parent--infant attachment**                                                                                                                                                                                                                                                                                                                                                                                                  

  Charpak et al[@b48-phmt-6-015]                            Sample: 82--406 LBW\                                                            RCT                                                                                      Mother                                                                  Mother's perception of\                                                                                             KC \> control (MD, 95% CI): Mothers' perceptions: sense of competence 1--2 days post birth (0.41, 0.14--0.68); sense of competence, infant admitted to NICU (0.54, 0.05--0.43); sense of competence, infant not admitted to NICU (0.24, 0.05--0.43); worry and stress free at 1--2 days (0.31, 0.04--0.58); social support at 14 days (−0.47, −0.84, −0.10); social support, infant not admitted to NICU (−0.20, −0.39, −0.01)\
                                                            Mode of delivery: V, C/S\                                                                                                                                                                                                                        premature birth questionnaire (1--5) and nursing child assessment feeding scale                                     Feeding scale: mothers sensitivity at 14 days (0.06, 0.01--0.11);\
                                                            Setting: tertiary center, Colombia                                                                                                                                                                                                                                                                                                                                   Responsiveness, 14 days (0.05, 0.01--0.09)\
                                                                                                                                                                                                                                                                                                                                                                                                                                 KC \> SC (MD 0.79, 95% CI 0.74--0.84)

                                                            338 LBW                                                                                                                                                                                                                                          HOME[b](#tfn2-phmt-6-015){ref-type="table-fn"} environment total score                                              No data reported on fathers, but author claims increased involvement

  Gathwala et al[@b47-phmt-6-015]                           Sample: 100 LBW (mean GA 35 weeks)\                                             RCT: KC 6 hours/day versus SC                                                            Mother                                                                  Mother--infant attachment at 3 months                                                                               KC \> control (MD 6.24, 95% CI 5.57--6.91)
                                                            Mode of delivery: V (81), C/S (9)\                                                                                                                                                                                                                                                                                                                                   
                                                            Setting: India                                                                                                                                                                                                                                                                                                                                                       

  Roberts et al[@b49-phmt-6-015]                            Sample: 30 LBW\                                                                 RCT: KC versus cuddling minimum 2 hours/day                                              Mother                                                                  Mother--infant attachment: stress in the NICU                                                                       Relationship with infant: KC \> control (MD 1.00, 95% CI 0.35--1.65)
                                                            Mode of delivery: N/A\                                                                                                                                                                                                                                                                                                                                               
                                                            Setting: Australia                                                                                                                                                                                                                                                                                                                                                   

  Neu and Robinson[@b50-phmt-6-015]                         Sample: 65 LBW 32--34 weeks GA\                                                 RCT: 1 hour a day of either holding in blanket or KC for 8 weeks                         Mother                                                                  Mother--infant interaction at 6 months                                                                              Symmetrical coregulation: KC \> control :\
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      (MD 16.38, 95% CI 13.61--19.1)\
                                                            Setting: five hospitals, USA                                                                                                                                                                                                                                                                                                                                         Asymmetrical coregulation: KC \< control\
                                                                                                                                                                                                                                                                                                                                                                                                                                 (MD −18.31, 95% CI −21.42, −15.20)

  Miles et al[@b51-phmt-6-015]                              Sample: n=79, \<32 weeks GA\                                                    Randomized crossover by site: 20 minutes KC daily ×4 weeks                               Mother                                                                  Infant interaction                                                                                                  No statistically significant difference
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: UK                                                                                                                                                                                                                                                                                                                                                          

  Tessier et al[@b26-phmt-6-015]                            Sample: 338, LBW\                                                               RCT: (70±40 minutes/day)                                                                 Mothers and fathers 24 hours/day until no longer tolerated by infants   HOME score                                                                                                          HOME score: KC \> mean score \[0.28 versus −0.51, F(1,330)=4.9, *P*\<0.03\], neurologically at-risk subgroup \[0.33 versus −1.09, *F*(1,330)=5.2, *P*\<0.03\], boys subgroup \[0.26 versus −1.02, *F*(1,330)=7.3, *P*\<0.001\]; KC families \> openness \[*F*(1,330)=3.9, *P*\<0.05\] boys and girls, girls only \[*F*(1,330)=9.4, *P*\<0.01\], neurologically at risk girls subgroup \[0.17 versus −0.87, *F*(1,330)=9.03, *P*\<0.01\]; KC \> for boys only subscales for responsiveness \[*F*(1,330)=9.1, *P*\<0.01\] more positive (less punitive) \[*F*(1,330)=3.5, *P*\<0.10\] and structured environment \[*F*(1,330)=5.3, *P*\<0.03\]; higher HOME scores correlated with infants' developmental quotient \[*F*(2,325)=5.6, *P*\<0.01\]
                                                            Mode of delivery: not reported\                                                                                                                                                                                                                                                                                                                                      
                                                            Setting: Colombia                                                                                                                                                                                                                                                                                                                                                    
  -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

**Notes:**

Stability of the Cardio-Respiratory system In Premature infants. Composite tool that indicates physiologic stability;

Home Observation for Measurement of the Environment,assesses quality and extent of stimulation available to a child in the home environment.

**Abbreviations:** LBW, low birth weight; NICU, neonatal intensive care unit; RCT, randomized controlled trial; KC, kangaroo care; MD, mean difference; V, vaginal; C/S, cesarean section; GA, gestational age; RR, relative risk; CI, confidence interval; HR, heart rate; hx, history; REM, rapid eye movement; EEG, electroencephalography; BF, breast feeding; BKC, birth kangaroo care; OR, odds ratio; N/A, not available; MEP, motor evoked potentials; PMA, postmenstrual age; SC, standard care; CG, control group; EBF, exclusive breastfeeding.

###### 

Benefits of kangaroo care in pain context

  --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Reference                                             Sample and setting                                        Design                                                                                                     Provider                    Outcome measures                                                                                    Results
  ----------------------------------------------------- --------------------------------------------------------- ---------------------------------------------------------------------------------------------------------- --------------------------- --------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------
  **Physiological stability**                                                                                                                                                                                                                                                                                                                                

  Johnston et al[@b11-phmt-6-015]                       121 preterm (four studies)\                               Meta-analysis of RCTs                                                                                      Mother\                     HR during and following painful procedure\                                                          No significant difference\
                                                        38 preterm (two studies)                                                                                                                                             Mother                      HRV during and following painful procedure measured using low, high, and low/high frequency ratio   No significant difference

  Johnston et al[@b54-phmt-6-015]                       Sample: n=74, 32--36 weeks GA\                            RCT crossover: 30 minutes of KC versus swaddled in incubator                                               Mother                      HR                                                                                                  No significant difference
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      
                                                        Setting: level III NICU, Canada                                                                                                                                                                                                                                                                      

  Johnston et al[@b64-phmt-6-015]                       Sample: 61 preterm (28--31 weeks GA)\                     RCT crossover: 15 minutes of KC before and during                                                          Mother                      Return to baseline HR, maximum HR, minimum oxygen levels                                            Return to baseline: KC \< SC (123 seconds, 95% CI 103--142 versus 193 seconds, 95% CI 158--227; *P*\<0.0000)\
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      Maximum HR: KC \< SC at 30, 60, and 90 seconds\
                                                        Setting: Canada                                                                                                                                                                                                                                                                                      Minimum oxygen levels: KC \> SC at 30, 60, and 90 seconds

  Nimbalkar et al[@b67-phmt-6-015]                      Sample: 47 preterm (32--36 weeks)\                        RCT: 15 minutes KC before, during, and after heel lance                                                    Mother                      HR, SpO~2~                                                                                          HR: KC \< KC\
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      SpO~2~: no difference
                                                        Setting: neonatal care unit, Karamsad, India                                                                                                                                                                                                                                                         

  Ludington-Hoe et al[@b66-phmt-6-015]                  Sample: 23 preterm (\<37 weeks GA)\                       RCT crossover: 3 hours KC before and during heel lance                                                     Mother                      SpO~2~                                                                                              No significant difference
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      
                                                        Setting: USA                                                                                                                                                                                                                                                                                         

  Cong et al[@b57-phmt-6-015]                           Sample: 28, 30--32 weeks GA\                              RCT: study a) 60 minutes KC, b) 10 minutes KC                                                              Mother                      Salivary and serum cortisol                                                                         Salivary cortisol: KC \< SC at end of recovery (*P*\<0.5)\
                                                        Mode of delivery: V (8), C/S (20)\                                                                                                                                                                                                                                                                   Serum cortisol: KC \< SC during heel lance
                                                        Setting: level II NICU in USA                                                                                                                                                                                                                                                                        

  Chidambaram et al[@b88-phmt-6-015]                    Sample: 47 preterm (32--46 weeks GA)\                     RCT crossover: 15 minutes KC                                                                               Mother                      HR, SpO~2~                                                                                          No significant difference
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      
                                                        Setting: South India                                                                                                                                                                                                                                                                                 

  **Pain score**                                                                                                                                                                                                                                                                                                                                             

  Johnston et al[@b11-phmt-6-015]                       30 seconds: 268 preterm (six studies)\                    Meta-analysis of RCTs                                                                                      Mother                      PIPP score at 30, 60, 90, and 120 seconds after painful procedure                                   30 seconds: KC \< SC (MD −3.21, 95% CI −3.94, −2.48)\
                                                        60 seconds: 164 preterm (four studies)\                                                                                                                                                                                                                                                              60 seconds: KC \< SC (MD −1.85, 95% CI −3.03, 0.068)\
                                                        90 seconds: 163 preterm (four studies)\                                                                                                                                                                                                                                                              90 seconds: KC \< SC (MD −1.34, 95% CI −2.56, −0.13)\
                                                        120 seconds: 156 preterm (four studies)                                                                                                                                                                                                                                                              120 seconds: no difference

  Cong et al[@b57-phmt-6-015]                           Sample: 28, 30--32 weeks GA\                              RCT: study a) 60 minutes KC, b) 10 minutes KC                                                              Mother                      PIPP scores 30, 60, 90, 120 seconds beyond the time of the procedure                                KC \< SC (between 8.12 and 0.4 points), greater differences the closer to the end of the procedure
                                                        Mode of delivery: V (8), C/S (20)\                                                                                                                                                                                                                                                                   
                                                        Setting: level II NICU in USA                                                                                                                                                                                                                                                                        

  Chidambaram et al[@b88-phmt-6-015]                    Sample: 47 preterm (32--46 weeks GA)\                     RCT crossover: 15 minutes KC                                                                               Mother                      PIPP score                                                                                          KC \< SC at 30 and 60 seconds (*P*=0.001)
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      
                                                        Setting: South India                                                                                                                                                                                                                                                                                 

  **Cry duration**                                                                                                                                                                                                                                                                                                                                           

  Johnston et al[@b11-phmt-6-015]                       Sample: 33 preterm (two studies)\                         Meta-analysis of RCT crossovers                                                                            Mother                      Cry duration                                                                                        No statistically significant difference
                                                        Setting: Canada                                                                                                                                                                                                                                                                                      

  **Sleep--wake state**                                                                                                                                                                                                                                                                                                                                      

  Ludington-Hoe et al[@b66-phmt-6-015]                  Sample: 23 preterm (\<37 weeks GA)\                       RCT crossover: 3 hours KC before heel lance                                                                Mother                      Sleep state during baseline and post stick                                                          Baseline: KC \> SC (*P*\<0.04)\
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      Post stick: KC \> SC (*P*\<0.05)
                                                        Setting: USA                                                                                                                                                                                                                                                                                         

  Cong et al[@b57-phmt-6-015]                           Sample: 26 preterm (28--32 weeks)\                        RCT crossover: 30 minutes\                                                                                 Mother                      Time in quiet sleep                                                                                 KC 30 and KC 15 minutes \> SC during recovery (*P*\<0.05)
                                                        Mode of delivery: V (3), C/S (20)\                        KC versus 15 minutes\                                                                                                                                                                                                                      
                                                        Setting: level III NICU, USA                              KC versus SC                                                                                                                                                                                                                               

  **KC versus alternative provider in pain context**                                                                                                                                                                                                                                                                                                         

  Johnston et al[@b11-phmt-6-015]                       Sample: 80 preterm                                        Meta-analysis of randomized crossover trials                                                               Father or unrelated woman   PIPP score at 30, 60, 90, and 120 seconds after painful stimulus                                    No statistically significant difference

  Johnston et al[@b63-phmt-6-015]                       Sample: 30s: 62 preterm (28--36 weeks GA)\                RCT crossover                                                                                              Father                      PIPP score at 30, 60, 90, and 120 seconds after painful stimulus, HR recovery                       No statistically significant difference
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      
                                                        Setting: level II NICU, Canada                                                                                                                                                                                                                                                                       

  Johnston et al[@b61-phmt-6-015]                       Sample: 16 preterm (28--37 weeks GA)\                     RCT crossover                                                                                              Unrelated woman             PIPP score at 30, 60, 90, and 120 seconds after painful stimulus, HR recovery                       No statistically significant difference
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      
                                                        Setting: level III NICU, Canada                                                                                                                                                                                                                                                                      

  **KC versus sweet taste in pain context**                                                                                                                                                                                                                                                                                                                  

  Freire et al[@b60-phmt-6-015]                         Sample: 95 preterm (28--36 weeks GA)\                     RCT: 10 minutes KC before, and during heel lance versus sweet taste 2 minutes before procedure versus SC   Mother                      PIPP score, HR variation, SpO~2~, duration of facial activity                                       HR variation: KC \< all (*P*=0.0001)\
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      SpO~2~: KC \< all (*P*=0.0012)\
                                                        Setting: university hospital, Brazil                                                                                                                                                                                                                                                                 Facial activity: KC \< all (*P*=0.0001)\
                                                                                                                                                                                                                                                                                                                                                             PIPP score: KC \< all (*P*=0.0001)

  **KC versus expressed breast milk in pain context**                                                                                                                                                                                                                                                                                                        

  Nanavati et al[@b89-phmt-6-015]                       Sample: 50 very LBW neonates, mean GA 32.33±1.34 weeks\   RCT, 15 minutes KC versus EBM for adhesive tape removal                                                    Mother                      PIPP score, HR, SpO~2~                                                                              No statistically significant difference
                                                        Mode of delivery: not reported\                                                                                                                                                                                                                                                                      
                                                        Setting: NICU, India                                                                                                                                                                                                                                                                                 

  **KC versus enhanced KC in pain context**                                                                                                                                                                                                                                                                                                                  

  Johnston et al[@b63-phmt-6-015]                       Sample: 90 preterm (32--36 weeks GA)\                     RCT crossover, 30 minutes KC before and during heel lance versus 30 minutes enhanced KC                    Mother                      PIPP at 30, 50, 90, and 120 seconds; HR return to baseline                                          No statistically significant difference
                                                        Mode of delivery: not specified                                                                                                                                                                                                                                                                      
  --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

**Abbreviations:** EBM, expressed breast milk; GA, gestational age; KC, kangaroo care; CI, confidence interval; MD, mean difference; HR, heart rate; HRV, heart rate variability; SpO~2~, oxygen saturation; PIPP, premature infant pain profile; RCT, randomized controlled trial; LBW, low birth weight; NICU, neonatal intensive care unit; V, vaginal; C/S cesarean section; SC, standard care.
