Spontaneous septostomy in a monochorionic-diamniotic twin gestation.

Monochorionic twin gestations are associated with a greater incidence of neonatal morbidity and mortality when compared with their dichorionic counterparts. In turn, monochorionic-monoamniotic (MCMA) gestations carry greater risks compared with monochorionic-diamniotic (MCDA) gestations. While the true incidence of spontaneous septostomy of the dividing membranes (SSDM) in MCDA twins is unknown, SSDM has been demonstrated to be associated with increased morbidity and mortality, due to functional transition from a MCDA gestation to a MCMA gestation. We report a case of SSDM in a mid-trimester MCDA gestation, review the literature, and describe how to identify and manage this complication.