Objective: The purpose of this series is to describe the prenatal diagnostic and management challenges of spontaneous septostomy of the dividing membrane (SSDM) in complicated monochorionic diamniotic (MoDi) pregnancies.
Methods: A retrospective review of all MoDi multiple gestations referred for fetal therapy was conducted. Spontaneous septostomy of the dividing membrane was suspected if a prior invasive procedure had not been performed and the following sonographic hallmarks were identified: twins occupying the same side of the dividing membrane, twin-twin transfusion syndrome (TTTS) with polyhydramnios in the donor's sac despite a collapsed donor bladder, and umbilical cord entanglement. Spontaneous septostomy of the dividing membrane was confirmed in all cases at the time of surgical fetoscopy, which was performed to treat an underlying condition of TTTS, selective intrauterine growth restriction (SIUGR), or the twin reversed arterial perfusion (TRAP) sequence.
Results: Of 217 complicated MoDi multiple gestations without prior invasive procedures referred for possible fetal therapy, 4 (1.8%) were identified with SSDM. The mean (range) gestational age at diagnosis was 19.7 (18-20.9) weeks. Two cases were diagnosed with TTTS complicated by SSDM after both fetuses were identified on the same side of the dividing membranes (1 case) or polyhydramnios was noted in the donor's sac despite a collapsed donor bladder (1 case). Both cases had substantial preoperative fetal deterioration because of a delay in diagnosis and treatment of TTTS. The remaining 2 SSDM cases, 1 with SIUGR and 1 with the TRAP sequence, were diagnosed after umbilical cord entanglement was recognized.
Conclusions: Spontaneous septostomy of the dividing membrane in MoDi gestations is a rare condition that poses diagnostic and management challenges.