Transvaginal Ultrasound Findings Predicting Prolonged Pregnancy in Cases of Prolapsed Fetal Membrane: A Retrospective Study

Background/Objectives: Fetal membrane prolapse can occur due to advanced cervical insufficiency. We investigated the yet unclear predictors of prolonged pregnancy in women with prolapsed fetal membranes. Methods: This retrospective observational study included 100 pregnant women with prolapsed fetal membranes between November 2017 and March 2023. We examined the correlation between transvaginal ultrasound findings at the time of admission and the duration of prolonged pregnancy, which was defined as the period from admission to delivery. We defined five transvaginal ultrasound indices: (1) width of the external os, (2) maximum width of the prolapsed fetal membrane, (3) distance from the external os to the presenting part of the fetus, (4) thickness of the posterior uterine lip, and (5) morphology of the prolapsed fetal membrane. Results: Women who underwent cervical cerclage comprised the cerclage group (n = 17), while those who underwent conservative management comprised the non-cerclage group (n = 83). The pregnancy period was significantly longer in the cerclage group than in the non-cerclage group (81.4 days vs. 9.1 days, p < 0.001). Multiple regression analysis revealed that type A morphology was a significant factor for prolonged pregnancy in the non-cerclage group (p < 0.05), which was significantly associated with a prolonged pregnancy period of over 7 days (p = 0.037). Conclusions: In cases of prolapsed fetal membranes, cerclage is challenging because of the high risk of iatrogenic preterm rupture of the membrane; however, if successful, a significant prolongation of the pregnancy period can be obtained. Morphological evaluation using ultrasonography is simple and easy to understand and correlates well with pregnancy outcomes, making it very useful.