Antepartum Management of Dichorionic/Diamniotic Twins
Chorionicity in twins is best determined by ultrasonography in the late first or early second trimester, with sensitivity of 90% or better. The twin peak sign (also called the lambda or delta sign) indicates dichorionicity and is a triangle shape at the base of the dividing membrane, with the same echogenicity of the chorion, best seen at 11-14 weeks. A thicker dividing membrane correlates well with dichorionicity. Dichorionicity can also be diagnosed if the fetuses are different gender or if two distinct placentas are seen. Monochorionicity is associated with significantly increased complications. Chorionicity is not the same as zygosity. Dichorionic diamniotic (di-di) twins may result from cleavage of a fertilized ovum within 72 hours of fertilization. Approximately 25-30% of monozygous twins are di-di.
Preterm birth occurs in more than 50% of twin gestations, with average gestational age of 36 weeks. Women with twins should be counseled regarding preterm delivery and associated neonatal morbidity. With any multifetal pregnancy, there is increased risk of hyperemesis, gestational diabetes, hypertension/preeclampsia, anemia, hemorrhage, fatty liver of pregnancy, cesarean delivery, and postpartum depression.
Congenital anomalies are increased 2-fold in twins compared to singletons, mainly occurring in monozygous twins. In dizygotic twins, each fetus has an independent risk for aneuploidy. The mathematical probability of aneuploidy increases with twins compared to singletons at any maternal age. First trimester screening for aneuploidy in twins utilizes sonographic evaluation of nuchal translucency. Serum screening in twin pregnancy is less sensitive due to averaging analytes from the fetuses. Cell free DNA testing in twins has been less extensively tested and does not specify the affected twin. An anatomy survey should be performed at 18-22 weeks.
Gestational age at delivery and fetal growth most influence neonatal outcome. Patients should be screened for signs and symptoms of preterm labor. Nutritional requirements for twin pregnancy are higher than for a singleton, with women of ideal body weight aiming for weight gains of 37-54 pounds. Additional iron and folate are recommended. The Institute of Medicine has published recommendations for pregnancy weight gain in twins based on pre-pregnancy BMI. Consultation with a dietician may be helpful.
Fetal growth scans of di-di twins are generally performed every 4 weeks starting after the 20 week anatomy survey. Routine antenatal surveillance does not improve outcomes and is reserved for pregnancies with complications or discordance. Growth discordance is an indication for closer surveillance.
Bedrest, outpatient uterine activity monitoring, routine fetal fibronectin screening, prophylactic tocolytics, prophylactic cervical cerclage, prophylactic pessary, and prophylactic progesterone administration are all ineffective for preventing preterm delivery. Use of vaginal progesterone for shortened cervix with twins is controversial. In cases of preterm labor, antenatal corticosteroids and magnesium for neuroprotection should be administered for the same indications as singleton gestations. The benefit of late preterm steroid administration (34 0/7 – 36 6/7 weeks) is unknown for multiple gestations. When indicated, calcium channel blockers and nonsteroidal anti-inflammatory drugs should be considered first-line tocolytics. If intrauterine demise of one twin in di-di pregnancy occurs, the surviving twin is managed expectantly. Disseminated intravascular coagulation is theoretically possible, but rare. Antepartum testing is indicated.
Due to earlier risk of stillbirth than singletons, uncomplicated di-di twins are delivered at 38 weeks, at the nadir for perinatal mortality. Early delivery should only be performed when indicated. Pregnancy prolongation after 39 weeks is not recommended.
Committee on Practice Bulletins—Obstetrics; Society for Maternal–Fetal Medicine; Practice Bulletin No. 169: Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies. Obstet Gynecol. 2016 Oct;128(4):e131-46. doi: 10.1097/AOG.0000000000001709.
Reddy U, Abuhamad A, Levine D, Saade F. et al; Fetal imaging: Executive summary of a Joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, American Institute of Ultrasound in Medicine, American College of Obstetricians and Gynecologists, American College of Radiology, Society for Pediatric Radiology, and Society of Radiologists in Ultrasound Fetal Imaging Workshop. Am J Obstet Gynecol. 2014 May;210(5):387-97. doi: 10.1016/j.ajog.2014.02.028.
ACOG Committee on Obstetric Practice. Committee Opinion No. 713: Antenatal Corticosteroid Therapy for Fetal Maturation., Obstet Gynecol. 2017 Aug;130(2):e102-e109. doi: 10.1097/AOG.0000000000002237.
Initial approval May /2016; Minor revisions 9/5/2017, Revised March 2019, Revised September 2019
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