Outcomes in twin pregnancies reduced to singleton pregnancies compared with ongoing twin pregnancies

OBJECTIVE: Multifetal pregnancy reduction has been shown to improve outcomes in triplet and higher-order multiple pregnancies. The data for fetal reduction of twin pregnancies are limited. The purpose of this study was to compare adverse pregnancy outcomes in ongoing twin pregnancies compared with twin pregnancies reduced to singletons. STUDY DESIGN: This was a retrospective cohort study comparing dichorionic diamniotic twin pregnancies with dichorionic diamniotic twin pregnancies reduced to singleton gestations between 11 and 24 weeks' gestation in a single maternal-fetal medicine practice over a 9 year period. Adverse pregnancy outcomes after 24 weeks were compared, with a value of P < .05 used for significance. RESULTS: Five hundred one ongoing twin pregnancies and 63 twin pregnancies reduced to singletons were included. Patients with reductions to singletons had a significantly lower risk of preterm delivery before 37 weeks' gestation (10% vs 43%; P < .001) but no difference in the risk of preterm delivery before 34 weeks' or 28 weeks' gestation. Patients with reductions to singletons also had a lower risk of infant birthweight less than the 10% (23% vs 49%; P < .001) but no difference in the risk of infant birthweight less than the 5%. There was no difference in the risk of fetal demise after 24 weeks' gestation. CONCLUSION: Fetal reduction of twin pregnancies decreases the risk of late preterm birth and birthweight less than the 10% but not the risks of more severe complications such as early preterm birth or birthweight less than the 5%.