Spontaneous rupture of the dividing membrane in a monochorionic pregnancy resulting in a pseudo-monoamniotic pregnancy with cord entanglement.

During pregnancy spontaneous rupture of the dividing membrane of monochorionic diamniotic twins is extremely rare and difficult to diagnose prenatally. We report a case of pseudo-monoamniotic twins derived from monochorionic diamniotic twin gestation. A 37-year-old woman pregnant with monochorionic diamniotic twins initially confirmed by the first trimester ultrasonography, was suspected to have a dividing membrane not visualized on ultrasound examinations at 27 gestational weeks. The woman did not undergo any invasive procedure during pregnancy and did not have notable symptoms. We considered the possibility of spontaneous rupture of the dividing membrane and cord entanglement, and managed the rest of her gestational period as a monoamniotic twin gestation. Concordantly grown healthy male babies were born at 35 weeks and 1 day by elective cesarean section. The mother had complex entangled umbilical cords and a small trace of amniotic membrane in the placenta.