Objective: We present 2 cases of spontaneous septostomy in dichorionic diamniotic twins and review the literature regarding the incidence, etiology, and complications of this condition.
Methods: The following key words were used in the literature search: "rupture dividing membrane twin," "disruption dividing membrane twin," "pseudomonoamniotic twin," "spontaneous septostomy twin," "interfetal membrane disruption," "intertwin membrane rupture," and "intertwin membrane disruption."
Results: We present 2 cases in which an intertwin membrane defect was found prenatally in dichorionic diamniotic twins. In both cases, a portion of one twin's body was found traversing the spontaneous septostomy and in the sac of its cotwin. Umbilical cord Doppler studies showed no abnormalities in either case as the cord crossed the membrane disruption. In both cases, the fetuses had no notable sequelae from the ruptured intertwin membrane. The literature review revealed no cases of spontaneous septostomy in dichorionic diamniotic twins but 15 cases in monochorionic diamniotic twins. Possible etiologies include chorioamnionitis, trauma or physical rupture by the fetuses, developmental disturbances represented by amniotic plica, and polyhydramnios. In cases of monozygotic twins, a vascular etiology could explain this rare defect with formation of anastomoses of the outer embryonic vasculature. Complications of the spontaneous septostomy cases identified in the literature included cord entanglement (8 cases), preterm delivery (9 cases), and death (8 cases), although our 2 cases had minimal complications.
Conclusions: Spontaneous septostomy in dichorionic diamniotic twins has not previously been reported.