Objective: To determine the optimum timing for planned delivery of uncomplicated monochorionic and dichorionic twin pregnancies.
Methods: Unselected twin pregnancies were recruited for this prospective cohort study (N=1,028), which was conducted in eight tertiary referral perinatal centers in Ireland. Perinatal mortality and a composite measure of perinatal morbidity (respiratory distress, necrotizing enterocolitis, hypoxic ischemic encephalopathy, periventricular leukomalacia, or sepsis) were compared between uncomplicated twins that underwent planned preterm delivery compared with monochorionic twins that continued in utero beyond 34 weeks of gestation, and dichorionic twins who continued beyond 36 weeks.
Results: Perinatal outcome data were recorded for 100% of the 1,001 twin pairs that completed the study (n=200 monochorionic and n=801 dichorionic). Overall perinatal mortality was 30 per 1,000 in monochorionic twins and 3.8 per 1,000 among dichorionic twins. The prospective risk of in utero death was 1.5% after 34 weeks of gestation for uncomplicated monochorionic pregnancies, with no deaths among dichorionic twins after 33 weeks. The risk of a composite measure of perinatal morbidity for uncomplicated monochorionic twins fell from 41% (13/32 neonates, 3/6 among elective deliveries) at 34 weeks to 5% (4/84) at 37 weeks (P<.001). Among dichorionic twins, the risk of morbidity fell from 4% (2/52) among elective deliveries at 36 weeks to 1% (5/344) in pregnancies continuing to 38 weeks (P=.231).
Conclusion: Applying a strategy of close fetal surveillance, perinatal morbidity can be minimized by allowing uncomplicated monochorionic pregnancies continue to 37 weeks of gestation and dichorionic twins to 38 weeks. Among monochorionic twins, this approach must be balanced against a 1.5% risk of late in utero death.