Supplementary Material for: Herniation of Ovular Membranes Through a Myometrial Defect Following Fetoscopic Laser Therapy for TTTS: An Underrecognized Maternal Complication

Introduction: Fetoscopy is a minimally invasive technique widely used for the treatment of twin-to-twin transfusion syndrome (TTTS), offering significant perinatal benefits. However, maternal complications of fetoscopy are underreported and incompletely characterized.

Case Presentation: We present the case of a 19-year-old primigravida with a monochorionic diamniotic pregnancy, diagnosed with Quintero stage II TTTS at 18 weeks of gestation, managed with fetoscopy and laser ablation. The clinical course remained stable until 30+3 weeks, 12 weeks after the fetoscopic procedure, when fetal demise of the donor twin and preterm labor were documented, prompting cesarean delivery. During surgery, a 5 mm myometrial defect was identified in the anterior-left lateral uterine wall, with herniation of ovular membranes through the defect at the site of the previous trocar insertion. This long interval between fetoscopy and detection of the defect is notably unusual.

Discussion: Herniation of ovular membranes through a myometrial defect is an uncommon complication following fetoscopy, typically associated with amniotic fluid leakage into the peritoneal cavity or unusual sonographic findings. In many cases, it may be asymptomatic and diagnosed incidentally during cesarean delivery, as occurred in our case. Given the delayed presentation, this report highlights the importance of prolonged surveillance. Comprehensive evaluation of both the fetus and the myometrial wall should be routine in patients undergoing fetoscopy.

Conclusion: The identification of a myometrial defect with herniation of ovular membranes 12 weeks after fetoscopy underscores the need for thorough ultrasound surveillance, including assessment of the fetus, amniotic fluid volume, and careful evaluation of the uterine wall and any unusual extrauterine findings.