Cervical Dilation and Risk of Delivery before 28 Weeks after Physical Exam-indicated Cerclage

To evaluate the association between the degree of cervical dilation at the time of physical exam-indicated cerclage and delivery before 28 weeks of gestation.

We conducted a retrospective cohort study of singleton pregnancies who underwent physical exam-indicated cerclage (painless cervical dilation ≥1 cm in the second trimester) at a single academic institution, 2014-2022. The primary outcome was delivery before 28 weeks. Cervical dilation was categorized as 1, 2, 3, and 4-5 cm. Multivariable logistic regression estimated adjusted odds ratios (aOR) with 95% confidence intervals (CI), adjusting for potential confounders. Kaplan-Meier analysis of the cerclage-to-delivery interval was examined as a sensitivity analysis.

Of 107 singleton pregnancies, 31 (29.0%) delivered before 28 weeks. Groups were similar except for BMI, which was higher among those who delivered before 28 weeks (34.6 ± 8.6 vs 30.8 ± 7.3 kg/m²; P=.026). Cervical dilation was greater in the early-delivery group (median 1.5 [IQR 1.0-3.0] vs 1.0 [IQR 1.0-2.0] cm; P=.016). Compared with 1 cm, dilation of 3 cm (aOR, 8.90; 95% CI, 1.75-45.30) and 4-5 cm (aOR, 12.95; 95% CI, 2.20-76.21) were independently associated with delivery before 28 weeks, whereas 2 cm was not (aOR, 0.74; 95% CI, 0.19-2.99); these estimates were imprecise because few patients had dilation of 3 cm or more. Median cerclage-to-delivery latency fell from 16.3 and 14.9 weeks at 1 and 2 cm to 2.4 and 1.5 weeks at 3 and 4-5 cm (log-rank P=.03).

Greater cervical dilation at physical exam-indicated cerclage was associated with delivery before 28 weeks in a dose-dependent manner, with an apparent inflection between 2 and 3 cm. Because the higher-dilation strata contained few patients, these associations should be interpreted with caution.