Guideline sources The following summarized guidelines for the evaluation and management of multiple gestation are prepared by our editorial team based on guidelines from the Society of Obstetricians and Gynaecologists of Canada (SOGC 2022; 2017; 2013), the American College of Medical Genetics (ACMG 2022), the American College of Obstetricians and Gynecologists (ACOG 2021; 2017), the International Federation of Gynecology and Obstetrics (FIGO 2021), the Royal College of Obstetricians and Gynaecologists (RCOG 2016), and the Society for Maternal-Fetal Medicine (SMFM 2013). 1 2 3 4 5 6 7 8 9 10 Guidelines 1. Screening and diagnosis https://web.pathway.md/diseases/recz0B3qo9upEgATC 1/8 6/30/23, 1:05 AM Multiple gestation Pathway Diagnosis of twin pregnancy: obtain a first-trimester ultrasound in all patients suspected to have or being at risk (such as pregnancies resulting from assisted reproductive technologies) of having a twin pregnancy on first-trimester physical examination. B Determination of gestational age: As per SOGC 2022 guidelines, use the measurements of the larger twin to determine the gestational age of a twin pregnancy. B Show 2 more As per SOGC 2017 guidelines, obtain a first-trimester ultrasound to determine the gestational age of a twin pregnancy. B Show 3 more As per RCOG 2016 guidelines, obtain an ultrasound examination between 11+0 and 13+6 weeks of gestation (crown-rump length 45-84 mm) to determine the gestational age of a twin pregnancy. B Determination of chorionicity and amnionicity: As per SOGC 2022 guidelines: Determine chorionicity during ultrasound assessment of all twin pregnancies, preferably at 11+0-13+6 weeks of gestation. A Assign labels to twins antenatally according to their lateral or vertical orientation rather than their proximity to the cervix. Assign labels to twins at the first ultrasound examination including other discriminating sonographic features that can help with the accuracy of labeling and maintain labels for all subsequent ultrasounds. Label the twin on the maternal right as twin A in laterally oriented twins. B As per SOGC 2017 guidelines: Attempt to determine and report amnionicity and chorionicity when a twin pregnancy is detected. B Use the deepest vertical pocket in either sac to define oligohydramnios (< 2 cm) and polyhydramnios oligohydramnios (> 8 cm). B As per RCOG 2016 guidelines, offer an ultrasound examination between 11+0 and 13+6 weeks of gestation (crown-rump length 45-84 mm) to assess chorionicity in all twin pregnancies. B Show 5 more 2. Classification and risk stratification Maternal and perinatal risks: As per ACOG 2017 guidelines: Recognize that multifetal pregnancies increase maternal and perinatal morbidity and mortality. Recognize that higher-order multifetal pregnancies present higher risks than twin pregnancies. E Recognize the medical risks of multifetal pregnancy, the potential medical benefits of multifetal pregnancy reduction, and the complex ethical issues inherent in decisions regarding multifetal https://web.pathway.md/diseases/recz0B3qo9upEgATC 2/8 6/30/23, 1:05 AM Multiple gestation Pathway pregnancy reduction. Be prepared to respond in a professional and ethical manner to patients requesting or declining to receive information or intervention, or both. E As per RCOG 2016 guidelines: Recognize that monochorionic twin pregnancies have higher fetal loss rates than dichorionic twin pregnancies mainly due to second-trimester loss and overall may have a higher risk of associated neurodevelopmental morbidity. B Recognize that monochorionic/dichorionic triplet pregnancies have higher fetal loss rates than trichorionic triplet pregnancies and may be complicated by twin-twin transfusion syndrome, selective growth restriction, and twin anemia polycythemia sequence. B 3. Diagnostic investigations Screening for chromosomal abnormalities, noninvasive testing: As per ACMG 2022 guidelines, obtain noninvasive prenatal screening for fetal trisomies 21, 18, and 13 in twin pregnancies. A As per SOGC 2017 guidelines, obtain fetal nuchal translucency combined with maternal age as first-trimester screening for aneuploidies in twin pregnancies. B Consider obtaining first- trimester serum screening combined with nuchal translucency, B or integrated screening with nuchal translucency and first- and second-trimester serum screening as another options in twin pregnancies. B Show 2 more As per SOGC 2017 guidelines, obtain aneuploidy screening using nuchal transluscency measurements in twin pregnancies. B As per RCOG 2016 guidelines: Obtain nuchal translucency measurements in conjunction with first-trimester serum markers (combined screening test) for aneuploidy screening at 11+0 to 13+6 weeks of gestation (crown-rump length 45-84 mm) in patients with monochorionic twins. B Obtain second-trimester screening by the quadruple test in patients with monochorionic twin pregnancies 'missing' or having unsuccessful first-trimester screening for aneuploidy. B Screening for chromosomal abnormalities (invasive testing): do not use maternal age alone as an indication for invasive prenatal diagnosis in twin pregnancies when noninvasive prenatal screening for aneuploidy is available. D . Offer invasive prenatal diagnosis in pregnant patients aged 35 years when noninvasive prenatal screening is not available. D Show 2 more Screening for structural abnormalities: As per SOGC 2017 guidelines, obtain a detailed ultrasound examination to screen for fetal anomalies, preferably at 18-22 weeks of gestation, in all twin pregnancies. B As per RCOG 2016 guidelines, obtain routine detailed ultrasound including extended views of the fetal heart anatomy between 18+0 and 20+6 weeks of gestation in all monochorionic twins. B https://web.pathway.md/diseases/recz0B3qo9upEgATC 3/8 6/30/23, 1:05 AM Multiple gestation Pathway Evaluation for discordant abnormalities: refer patients with monochorionic twins having discordant fetal anomalies to a fetal medicine center for assessment, counseling, and consideration for treatment. B Show 3 more Monitoring for selective intrauterine growth restriction: calculate estimated fetal weight discordance using 2 biometric parameters at each ultrasound from 20 weeks of gestation (at 2- weekly intervals) onwards. Calculate percentage estimated fetal weight discordance using the following formula: (difference between estimated fetal weights of larger and smaller twins/larger twin estimated fetal weight) 100. Measure and record liquor volumes as deepest vertical pocket (to differentiate from twin-twin transfusion syndrome). B Show 4 more Monitoring for twin-twin transfusion syndrome: as per RCOG 2016 guidelines, do not obtain screening for twin-twin transfusion syndrome by first-trimester nuchal translucency measurements. D Show 3 more Antenatal fetal monitoring: As per SOGC 2022 guidelines: Monitor fetal growth with ultrasound every 3-4 weeks starting at about 24 weeks gestation in uncomplicated dichorionic twin pregnancies. B Consider using twin-specific growth charts when using ultrasound biometry to assess growth velocity. B Measure cervical length (ideally transvaginally) at the anatomy ultrasound in patients with twin pregnancies and, if possible, once again before 24 weeks, since cervical length is a good predictor of the risk of preterm birth. B As per SOGC 2017 guidelines, do not obtain umbilical artery Doppler assessment routinely in uncomplicated twin pregnancies. D Show 2 more As per RCOG 2016 guidelines: Obtain fetal U/S assessments every 2 weeks, from 16+0 weeks onwards until delivery, in uncomplicated monochorionic pregnancies. B Obtain increased ultrasound surveillance of triplet pregnancies in a fetal medicine center with expertise to manage such cases. B 4. Nonpharmacologic interventions Bed rest: as per SOGC 2022 guidelines, do not advise bed rest or restriction of activity in patients with twin pregnancies, either in the presence or absence of risk factors for preterm birth. D Cervical pessary: as per SOGC 2022 guidelines, insufficient evidence to recommend the use of cervical pessaries in patients with a twin pregnancy and a short cervix. I https://web.pathway.md/diseases/recz0B3qo9upEgATC 4/8 6/30/23, 1:05 AM Multiple gestation Pathway 5. Therapeutic procedures Cervical cerclage: as per SOGC 2022 guidelines, consider performing cervical cerclage in asymptomatic patients with twin pregnancies when cervical length is 15 mm. C Perform cervical cerclage when cervical dilation is 1 cm before 24 weeks gestation. B Selective reduction: as per RCOG 2016 guidelines, discuss the option of selective reduction and make it available to patients requesting the procedure, after appropriate counseling, before invasive testing or in the context of twins discordant for an abnormality. B Show 3 more Management of delivery: As per SOGC 2022 guidelines, include a discussion of vaginal, Cesarean, and combined delivery in the informed consent for the mode of delivery of twins. Recognize that planned vaginal delivery carries no increased risk compared with planned Cesarean delivery. A Show 7 more As per RCOG 2016 guidelines, offer elective delivery from 36+0 weeks of gestation with the administration of antenatal corticosteroids in patients with monochorionic twins, unless there is an indication to deliver earlier. B Show 3 more 6. Specific circumstances Patients with selective intrauterine growth restriction (diagnosis): Base the definition of fetal growth restriction on a combination of measures of fetal size percentile and Doppler abnormalities. B Take into consideration intertwin size discordance when diagnosing fetal growth restriction in twin gestations, especially in the case of monochorionic placentation. A Consider using twin-specific charts for the assessment of fetal growth in twin gestations to avoid overdiagnosis of fetal growth restriction in this population. C Patients with selective intrauterine growth restriction, management: As per RCOG 2016 guidelines, consider offering selective reduction in patients with early-onset selective IUGR in association with poor fetal growth velocity and abnormal umbilical artery Doppler assessments. C Show 6 more As per SOGC 2013 guidelines, initiate low-dose aspirin between 12 and 16 weeks of gestation and continue until 36 weeks in patients with multiple gestation and 1 current risk factor including but not limited to: maternal age > 40 years obesity pre-gestational hypertension pre-gestational diabetes mellitus (type 1 or 2) https://web.pathway.md/diseases/recz0B3qo9upEgATC 5/8 6/30/23, 1:05 AM Multiple gestation Pathway history of artificial reproductive technology use history of placental abruption history of placental infarction. A Patients with twin-twin transfusion syndrome (diagnosis): Diagnose twin-twin transfusion syndrome based on the presence of the following: monochorionic diamniotic pregnancy oligohydramnios (a maximum vertical pocket of < 2 cm) in one sac, and of polyhydramnios (a maximum vertical pocket of > 8 cm) in the other sac. B Patients with twin-twin transfusion syndrome, evaluation: As per RCOG 2016 guidelines: Use the Quintero system to stage twin-twin transfusion syndrome at diagnosis, and additionally, measure umbilical artery Doppler velocities and obtain middle cerebral artery PSV and ductus venosus Doppler studies. B Screen for twin anemia polycythemia sequence following fetoscopic laser ablation for twin-twin transfusion syndrome and in other complicated monochorionic pregnancies requiring referral to a fetal medicine center (such as complicated by selective growth restriction) by serial middle cerebral artery PSV. B As per SMFM 2013 guidelines, consider using the Quintero staging system for the assessment of twin-twin transfusion syndrome severity. C Show 2 more Patients with twin-twin transfusion syndrome, management: As per RCOG 2016 guidelines, perform fetoscopic laser ablation (using the Solomon technique) rather than amnioreduction or septostomy for the treatment of twin-twin transfusion syndrome presenting before 26 weeks of gestation. A Show 5 more As per SMFM 2013 guidelines, provide extensive counseling including natural history of the disease, as well as management options (expectant management, amnioreduction, intentional septostomy of the intervening membrane, fetoscopic laser photocoagulation of placental anastomoses, selective reduction, and pregnancy termination) and their risks and benefits in patients with pregnancies complicated by twin-twin transfusion syndrome. Recognize that over three fourth of stage I twin-twin transfusion syndrome cases remain stable or regress without invasive interventions, while the natural history of advanced (stage III) twin-twin transfusion syndrome is bleak, with a reported perinatal loss rate of 70-100%, particularly when it presents < 26 weeks. B Show 4 more Patients with single fetal demise: recognize that monochorionic pregnancies not complicated by twin-twin transfusion syndrome, selective growth restriction, or twin anemia-polycythemia sequence are still at risk of fetal death and neurological abnormality. B Show 4 more https://web.pathway.md/diseases/recz0B3qo9upEgATC 6/8 6/30/23, 1:05 AM Multiple gestation Pathway Patients with conjoined twins: obtain prenatal assessment in a tertiary fetal medicine center to confirm the diagnosis of conjoined twins. Discuss prognosis in conjunction with a multidisciplinary team as conjoined twins are exceedingly rare. B 7. Patient education General counseling: As per ACOG 2017 guidelines, provide nondirective counseling in all patients with higher-order multifetal pregnancies and include a discussion of the risks unique to multifetal pregnancy as well as the option to continue or reduce the pregnancy. Consider including maternal-fetal medicine specialists, neonatologists, mental health professionals, child development specialists, support groups, and clinicians with procedural expertise in multifetal pregnancy reduction for providing such counseling. E Show 2 more As per RCOG 2016 guidelines, inform patients with monochorionic twin pregnancies that they have higher fetal loss rates compared with dichorionic twin pregnancies mainly due to second- trimester loss and overall may have a higher risk of associated neurodevelopmental morbidity. B 8. Preventative measures Primary prevention: recognize that fertility treatments have contributed significantly to the increase in multifetal pregnancies. Consider implementing primary prevention strategies in the treatment for infertility to limit multifetal pregnancies, especially higher-order multifetal pregnancies, to minimize the need for multifetal pregnancy reduction. E 9. Quality improvement Ultrasound operator requirements: train all sonographers undertaking routine ultrasound during pregnancy to establish chorionicity and the correct labeling of twins. B Show 2 more Clinical findings Past medical history Past obstetric history Low birth weight Assisted reproductive technology Obesity Fetal anemia Preterm birth Fetal trisomies IUGR https://web.pathway.md/diseases/recz0B3qo9upEgATC 7/8 6/30/23, 1:05 AM Multiple gestation Pathway IVF Preeclampsia T i t i t f i d References 1. Lucie Morin, Kenneth Lim. No. 260 Ultrasound in Twin Pregnancies. J Obstet Gynaecol Can. 2017 Oct;39 10):e398-e411. Open 2. Society for Maternal-Fetal Medicine, Lynn L Simpson. Twin-twin transfusion syndrome. Am J Obstet Gynecol. 2013 Jan;208 1 3 18. Open 3. Green-top Guideline No. Management of Monochorionic Twin Pregnancy. RCOG. 2016 Nov 16;. Open 4. Elad Mei-Dan, Venu Jain, Nir Melamed et al. Guideline No. 428 Management of Dichorionic Twin Pregnancies. J Obstet Gynaecol Can. 2022 Jul;44 7 819 834.e1. Open 5. ACOG Practice Bulletin, Number. Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies. ACOG. 2021 Jun;. Open 6. Jeffrey S Dungan, Susan Klugman, Sandra Darilek et al. Noninvasive prenatal screening NIPS for fetal chromosome abnormalities in a general-risk population: An evidence-based clinical guideline of the American College of Medical Genetics and Genomics ACMG . Genet Med. 2022 Dec 13;S1098 3600 22 01004 8. Open 7. Andrea Lausman, John Kingdom, MATERNAL FETAL MEDICINE COMMITTEE. Intrauterine growth restriction: screening, diagnosis, and management. J Obstet Gynaecol Can. 2013 Aug;35 8 741 748. Open 8. American College of Obstetricians and Gynecologists. Committee Opinion No. 719 Multifetal Pregnancy Reduction. Obstet Gynecol. 2017 Sep;130 3):e158-e163. Open 9. Fran ois Audibert, Alain Gagnon. No. 262 Prenatal Screening for and Diagnosis of Aneuploidy in Twin Pregnancies. J Obstet Gynaecol Can. 2017 Sep;39 9):e347-e361. Open 10. Nir Melamed, Ahmet Baschat, Yoav Yinon et al. FIGO International Federation of Gynecology and Obstetrics) initiative on fetal growth: best practice advice for screening, diagnosis, and management of fetal growth restriction. Int J Gynaecol Obstet. 2021 Mar;152 Suppl 1 Suppl 1 3 57. Open https://web.pathway.md/diseases/recz0B3qo9upEgATC 8/8