Abstract
Spontaneous septostomy of the dividing membrane in monochorionic diamniotic twins（MD twins）is rare. When there is a spontaneous septostomy of the dividing membrane, in addition to complications unique to MD twins, attention must be paid to umbilical cord entanglement. We recently reported a case of spontaneous septostomy of the dividing membrane in an MD twin. The case involved a 27-year-old, G1P0, naturally conceived pregnant woman who was referred to our hospital at nine gestational weeks and confirmed to have MD twins through ultrasound examination. At 19 gestational weeks, umbilical cord entanglement was visualized on ultrasonography; therefore, we considered the possibility of a spontaneous septostomy of the dividing membrane. She was diagnosed with selective intrauterine growth restriction（selective IUGR）type 3 at 24 weeks of gestation. Considering the risk of umbilical cord entanglement, an elective cesarean section was planned at 33 gestational weeks. At 32 weeks and three days of gestation, frequent variable deceleration was observed in the fetuses, with fetal growth restriction（FGR）during fetal heart rate monitoring. Emergency cesarean section was performed for non reassuring fetal status, which resulted in the birth of live babies. Umbilical cord entanglement was confirmed during surgery, and a dividing membrane was found in the placenta. There are a few reports on the natural rupture of membranes in MD twins, and further knowledge is expected to improve our understanding of this in the future.
