Twins account for 3.3 percent of all births in the United States. This near doubling of the incidence since 1980 is attributable to advancing maternal age at conception and increasing use of assisted reproductive technology (American College of Obstetricians and Gynecologists, 2014a). During roughly the same period, the cesarean delivery rate for twins has increased to 75 percent, thereby reducing the overall experience with vaginal delivery of twins (Lee, 2011). Germane to this, an obstetric care consensus developed jointly by the American College of Obstetricians and Gynecologists (2014b) and the Society for Maternal-Fetal Medicine concluded that perinatal outcomes when the first twin presents cephalic are not improved by cesarean delivery. This document states that for twins with cephalic/cephalic or cephalic/noncephalic presentations, obstetric care providers should counsel women to attempt vaginal delivery. Such a strong recommendation assumes that residents are being trained to perform vaginal twin deliveries and that practicing clinicians are sufficiently competent and confident to manage the labor and delivery of such women (Carroll, 2006). The goal of this chapter is to present a well-illustrated approach to the vaginal delivery of twins.
Twin gestation presents a broad array of maternal, fetal, and neonatal complications, some of which are related to the intrapartum period and some that are not. Gestational hypertension or preeclampsia complicates up to 20 percent of twin pregnancies (Fox, 2015). Postpartum hemorrhage due to uterine atony is more common with multifetal gestations because the uterus is overdistended. Compared with those for singletons, rates for stillbirth are nearly threefold higher, for neonatal death are sevenfold higher, and for very low birthweight (<1500 grams) are 11-fold higher in twins (Cunningham, 2014).
Of twins, 16 percent have weight discordance of at least 20 percent (Miller, 2012). Discordance is expressed as a percent and defined by the formula below.
Some cases of discordance are caused by fetal growth restriction of the smaller twin, and severe growth restriction increases the risk of mortality. If twin B is more than 25-percent larger than twin A, the planned route of delivery may need to be reconsidered.
Arguably, the most significant complication is preterm birth, occurring in more than 50 percent of twin gestations. Clearly, preterm birth of twins is a major contributor to overall neonatal morbidity and mortality. Congenital anomalies are more frequent in twins and constitute a second important contributor to adverse outcomes.
For this chapter, the appropriate focus is on intrapartum complications. This was the approach taken in the Twin Birth Study (Barrett, 2013). This large randomized trial defined a composite outcome that incorporated serious neonatal morbidity and fetal or neonatal mortality. Serious morbidity was birth trauma, birth asphyxia, neonatal seizures, requirement for resuscitation or intubation, intraventricular hemorrhage, and admission to a neonatal intensive care unit. Notably, in this large trial, composite outcome ...