Alexis Shub, Susan P Walker

Monoamniotic twin pregnancies are formed when a single egg is fertilised and the resulting inner cell mass splits to form twins sharing the same amniotic sac. This condition is rare and affects about one in 10,000 pregnancies overall. Monoamniotic twin pregnancies are susceptible to complications including cord entanglement, increased congenital anomalies, intrauterine growth restriction, twin-to-twin transfusion syndrome and increased perinatal mortality. All twin pregnancies also carry additional maternal risks including pre-eclampsia, anaemia, antepartum haemorrhage, postpartum haemorrhage and operative delivery.The optimal timing for the delivery of monoamniotic twins is not known. The options include 'planned early delivery' between 32 and 34 weeks, or alternatively awaiting spontaneous labour at least up until the usual time of planned delivery for other monochorionic twins (approximately 36 to 38 weeks' gestation), unless there is a specific indication for earlier delivery. To assess whether routine early delivery in monoamniotic twin pregnancies improves fetal, neonatal or maternal outcomes compared with 'expectant management'. Expectant management means awaiting spontaneous labour at least up until the usual time of planned delivery for other monochorionic twins (approximately 36 to 38 weeks' gestation in many centres), unless a specific indication for delivery occurs in the meantime, e.g. for non-reassuring antenatal testing. We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 March 2015). Published and unpublished randomised controlled trials (including cluster-randomised trials) comparing outcomes for women and infants who were randomised to planned early delivery of a monoamniotic twin pregnancy with outcomes for women and infants who were randomised to either planned term delivery or expectant management. However, we did not identify any trials for inclusion in this review.Quasi-randomised controlled trials, trials published in abstract form only, and trials using a cross-over design are not eligible for inclusion in this review. No trials were identified by the search strategy. No trials were identified by the search strategy. Monoamniotic twins are rare, and there is insufficient randomised controlled evidence on which to draw strong conclusions about the best management. In their absence, we can refer to historical case series and expert consensus. Management plans should take into consideration the availability of high-quality neonatal care if early delivery is chosen. Women and their families should be involved in the decision making about these high-risk pregnancies.Ongoing, multicentre audits of maternal and perinatal outcomes for monoamniotic twins are needed in order to inform families and clinicians about up-to-date perinatal outcomes with contemporary obstetric practice. Research should consider the social and economic implications of planned interventions, as well as the perinatal outcomes.