Monochorionic monoamniotic twin pregnancies.

Abstract

Monochorionic monoamniotic (MCMA) twin pregnancy is rare and associated with increased complication rates when compared with singletons, dichorionic and monochorionic diamniotic pregnancy in general. Monoamnionicity presents an enormous challenge following its accurate diagnosis, where the absence of an inter-twin membrane subsequently results in cord entanglement and consistently fluctuating foetal position. Furthermore, the detection of twin-twin transfusion syndrome (TTTS) in MCMA pregnancy can be challenging in the absence of amniotic fluid volume discordance without the presence of the inter-twin dividing membrane. Early surveillance of foetal anatomy permits early recognition of foetal structural anomalies, the twin reversed arterial perfusion (TRAP) sequence and conjoined twins. However, the evidence on how best to monitor MCMA pregnancies remains inadequate, though observational studies have demonstrated that once surveillance is initiated, the potential risk of foetal death decreases significantly. In-utero foetal demise can be acute and unpredictable in MCMA pregnancies, despite close surveillance. Elective preterm delivery is usually advocated when the risk of foetal loss upon continuing the pregnancy outweighs the risk of prematurity - around 33 weeks' gestation by caesarean section. Nevertheless, the optimal prenatal surveillance regimen and prompts for delivery have yet to be defined.