Antepartum Management of Dichorionic/Diamniotic Twins
5/4/2016 - Marygrace Elson, MD
Editor: Pamela D. Berens, MD
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) is a triangle shape extending above the surface, with the same echogenicity of the chorion, best seen at 11-14 weeks and indicates dichorionicity. The dividing membrane may also be measured. 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 at < 72 hrs. 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 mellitus, 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 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 given 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 normal and affected fetuses. Cell free DNA testing in twins is less extensively tested and also 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 gain of 37-54 pounds. Additional iron and folate are suggested. 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 after the 20 week anatomy survey. Routine antenatal surveillance does not improve outcomes, and is reserved for complications or discordance. Growth discordance is an indication for closer surveillance. Decisions regarding delivery are based on tests of fetal well-being and gestational age.
Bedrest, outpatient uterine activity monitoring, routine fetal fibronectin screening, prophylactic tocolytics, prophylactic cervical cerclage, prophylactic pessary, and prophylactic progesterone administration are all ineffective. Vaginal progesterone for shortened cervix with twins is controversial. If intrauterine demise occurs of one twin in di-di pregnancy 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 is for indications only. Prolongation after 39 weeks is not advised.
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