Diagnosis and management of two cases of spontaneous septostomy: monochorionic/dichorionic hybrid twin gestation and dichorionic triamniotic triplet gestation

Introduction: Spontaneous septostomy is a rare complication of multiple gestations. Related complications include cord entanglement and preterm delivery. Limited data exists to guide management of these high-risk patients. The majority of spontaneous septostomy cases have been reported in monochorionic diamniotic twins. We present two cases of spontaneous septostomy occurring in a monochorionic/dichorionic hybrid twin gestation (chorionicity transitions from dichorionicity to monochorionicity within the placenta) and in a dichorionic triamniotic triplet gestation.Case Presentation: Case 1 was a monochorionic/dichorionic hybrid twin gestation with a septostomy complicated by fetal parts of one twin protruding into the co-twin's sac as well as symptomatic polyhydramnios. Fetal MRI confirmed the septostomy. Case 2 was a dichorionic triamniotic triplet gestation with septostomy and cord entanglement. Both patients were managed akin to a pseudo-monoamniotic gestation with serial ultrasound surveillance and eventual inpatient admission for heightened fetal monitoring. Case 1 underwent elective scheduled cesarean delivery at 33 weeks and Case 2 underwent emergent cesarean delivery for fetal heart rate decelerations at 28 weeks.Conclusion: With a high degree of clinical suspicion, spontaneous septostomy can be diagnosed in uncommon settings such as hybrid twin gestations and higher order multiples. Management of such patients is individualized and may include a combination of heightened outpatient and inpatient surveillance.