Cervical length following cerclage as a predictor of spontaneous preterm birth

We aimed to evaluate the association between serial transvaginal cervical length measurements following McDonald cerclage and spontaneous preterm birth (PTB).

This retrospective study included singleton pregnancies with cerclage performed during 2010-2024. Cerclage was placed prophylactically (n = 109) based on obstetric history, or emergently (n = 46) due to ultrasound findings. Cervical length was measured by transvaginal ultrasound before and after cerclage, and at 2-week intervals until 32 weeks.

For the prophylactic group, the median cervical length was shorter among those who delivered PTB < 37 weeks (n = 23) than term: at 21-22 + 6 weeks (2.5 vs. 3.9 cm, p = 0.042), 23-24 + 6 weeks (2.0 vs. 3.4 cm, p = 0.016), 25-26 + 6 weeks (3.0 vs. 3.8 cm, p = 0.042), and 31-32 + 6 weeks (2.4 vs. 3.4 cm, p = 0.015). In multivariable analysis adjusted for history of PTB, progesterone use, and gestational age at cerclage placement, shorter cervical length, at 23-24 + 6 weeks (adjusted odds ratio [aOR] 4.13, 95% confidence interval [CI] 1.23-13.89, p = 0.021) and at 25-26 + 6 weeks (aOR 3.39, 95% CI 1.08-10.64, p = 0.037), was independently associated with PTB < 37 weeks. Cervical length at 25-26 + 6 weeks was associated with PTB < 32 weeks (aOR 4.76, 95% CI 1.20-19.60, p = 0.027). For the emergency group, the median cervical length was shorter among those who delivered < 32 weeks than later, at 23-24 + 6 weeks (1.4 vs. 3.2 cm, p = 0.049) and 25-26 weeks (1.5 vs. 2.3 cm, p = 0.041).

Serial cervical length monitoring after cerclage provides a clinically relevant prediction of spontaneous PTB.