FIGURE 42-6 Neonatal death rates at Parkland Hospital from 34 to 40 weeks' gestation in singleton infants without malformations. ap <0.001 compared with 39 weeks as the referent. bp = 0.02 compared with 39 weeks as the referent. (Reproduced with permission from Mcintire DO, Leveno J: Neonatal mortality and morbidity rates in later preterm births compared with births at term, Obstet Gynecol. 2008 Jan;lolol (1 ):35-41.) idiopathic spontaneous preterm labor or prematurely ruptured membranes (Fig. 42-5). Other obstetrical complications were implicated in the remaining 20 percent of cases. Rates of morbidity and mortality were greater in these late-preterm newborns compared with rates in term ones (Table 42-5 and Fig. 42-6). Similarly, T omashek (2017) also reported higher neonatal mortality rates for late-preterm newborns. Rates of
TABLE 42-5. Neonatal Morbidity Rates at Parkland Hospital in Live Births Delivered Late Preterm Compared with 39 Weeks
Grades 1,2
Grades 3,r4 Sepsis
One or more of the above aData presented as n (%).
bp <.001 compared with 39 weeks referent. cp <.05 compared with 39 weeks referent. Reproduced with permission from Mcintire DO, Leveno IJ: Neonatal mortality and morbidity rates in later preterm births compared with births at term, Obstet Gynecol. 2008 Jan;lnll (1 ):35-41r.
adverse neurodevelopment outcomes are also increased in these late-preterm infants (Petrini, 2009).
Taken together, these findings suggest that a health-care focus on prematurity should include these late-pre term births.
Moreover, approximately 80 percent of afected women begin labor spontaneously-similar to births before 34 weeks-and attempts to interrupt preterm labor have been insuicient (Institute of Medicine, 2007). Because of this, a national strat egy aimed at prevention of late-preterm births is unlikely to provide discernible benefit without new developments in the prevention and management of preterm labor. In the mean time, the American College of Obstetricians and Gynecolo for delivery exists.
Four direct causes for preterm births in the United States include: (1) spontaneous unexplained preterm labor with intact membranes, (2) idiopathic preterm premature rupture of membranes (PPROM), (3) delivery for maternal or fetal indications, and (4) twins and higher-order multi fetal births. Of all preterm births, 30 to 35 percent are indicated, 40 to 45 percent are due to spontaneous preterm labor, and 30 to 35 percent follow preterm membrane rupture (Goldenberg, 2008). Indeed, much of the increase in the singleton preterm birth rate in the United States is explained by rising numbers of indicated preterm births (Ananth, 2005). Last, more than one of every two twins and more than nine of every ten triplets are born preterm or with low birthweight in the United States (Chap. 45, p. 873) (Martin, 2017).
Reasons for preterm birth have multiple, often interacting, antecedents and contributing factors (Esplin, 2016). This is particularly true for PPROM and spontaneous preterm labor.