Antepartum Management of Dichorionic/Diamniotic Twins
Chorionicity in twins is determined by ultrasonography in the late first or early second trimester, with sensitivity of 90% or better. The twin peak sign (lambda or delta sign) indicates dichorionicity. A thicker dividing membrane suggests dichorionicity. Dichorionicity is diagnosed if the fetuses are different sex or if two distinct placentas are seen.
Preterm birth occurs in more than 50% of twin gestations, with average gestational age of 36 weeks. Twins born preterm (<32 weeks) have twice the risk of high-grade intraventricular hemorrhage and periventricular leukomalacia as compared to singletons of the same gestation. People with twins should be counseled regarding preterm delivery and associated neonatal morbidity. Multifetal gestation is associated with increased risk of hyperemesis, gestational diabetes, hypertension, anemia, hemorrhage, fatty liver of pregnancy, cesarean delivery, and postpartum depression. Low dose aspirin is recommended in multifetal gestations to mitigate the risk of pre-eclampsia.
Congenital anomalies are increased 2-fold in twins compared to singletons, mainly occurring in monozygotic twins. Aneuploidy risk 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. Cell free DNA testing in twins has been less extensively tested and cannot specify the affected twin. Sensitivity for Trisomy 21 may be comparable to singletons when results are returned, but there is a higher rate of test failure. 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 gain of 37-54 pounds. Additional iron and folate are recommended.
Fetal growth scans of di-di twins are generally performed every 4 weeks starting after the 20 week anatomy survey. Stillbirth rates are higher in dichorionic twins than in singletons, and weekly antenatal surveillance may be considered at 36 0/7 weeks in uncomplicated dichorionic pregnancies. In pregnancies complicated by maternal or fetal conditions, surveillance is considered at diagnosis or when abnormal testing may prompt delivery.
Bedrest, outpatient uterine activity monitoring, routine fetal fibronectin screening, and prophylactic tocolytics, cerclage, pessary, or progesterone 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 possible, but rare. Antepartum testing is indicated.
Due to earlier risk of stillbirth than singletons, uncomplicated di-di twins are delivered at 38 weeks. Earlier delivery should only be performed when indicated. Pregnancy prolongation after 39 weeks is not recommended.
American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics, Society for Maternal-Fetal Medicine. Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies: ACOG Practice Bulletin, Number 231. Obstet Gynecol. 2021 Jun 1;137(6):e145-e162. doi: 10.1097/AOG.0000000000004397. PMID: 34011891.
Bodnar LM, Himes KP, Abrams B, et al. Gestational Weight Gain and Adverse Birth Outcomes in Twin Pregnancies. Obstet Gynecol. 2019 Nov;134(5):1075-1086. doi: 10.1097/AOG.0000000000003504. PMID: 31599828; PMCID: PMC6814560.
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. PMID: 28742678.
Initial approval May /2016; Minor revisions 9/5/2017, Revised March 2019, Revised September 2019, Revised March 2022
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