Abstract
Spontaneous septostomy of the dividing membrane is a rare complication of monochorionic diamniotic twin gestation. Although antenatal diagnosis is preferable, the cause of spontaneous septostomy as well as its diagnostic criteria and management have not been clarified. We experienced two cases of spontaneous septostomy in monochorionic diamniotic twins with proximate umbilical cord insertion. Case 1 was diagnosed as spontaneous septostomy at 25 weeks’ gestation, and umbilical cord entanglement could not be confirmed. Case 2 was diagnosed at 20 weeks’ gestation, and cord entanglement was suspected. Selective cesarean section was performed at 34 weeks’ gestation, and all babies were born healthy. The umbilical cord insertion sites were close in both cases, but cord entanglement was observed only in case 2. Proximate umbilical cord insertion was observed in 90％ of previous cases, which is characteristic of spontaneous septostomy in monochorionic diamniotic twins and seems useful for diagnosis and risk recognition. Since it is difficult to estimate fetal risk due to the timing of diagnosis or presence of umbilical cord entanglement, antenatal diagnosis of septostomy and careful management are important.
