Identifying a critical cervical length threshold for predicting early delivery at 24–34 weeks

Objective This study evaluates the association between cervical length measured at first diagnosis of a short cervix and delivery within 14 days among symptomatic and asymptomatic singleton pregnancies at 24 0/7 –33 6/7 weeks of gestation. Methods A retrospective cohort study was conducted comprising singleton pregnancies diagnosed with a short cervix (≤ 25 mm) at 24 0/7 –33 6/7 weeks, including both symptomatic and asymptomatic women. The primary outcome was spontaneous delivery within 14 days with delivery within 7 days as a secondary outcome. The optimal cervical length (CL) threshold was identified using Youden's index and internally validated. Predictors for delivery within 14 days were analyzed using multivariable logistic regression. Results Among 1027 pregnancies, 94 (9.2%) delivered within 14 days and 53 (5.2%) within 7 days. CL was significantly associated with gestational age at delivery ( P < 0.001). A CL of ≤ 14 mm was the optimal threshold for both outcomes (14 days: area under the receiver operating characteristic curve [AUC] 0.59, 95% confidence interval [CI] 0.52–0.65, sensitivity 38.3%, specificity 79.0%, positive predictive value 15.5%, negative predictive value 92.7%; 7 days: AUC 0.65, 95% CI 0.57–0.73). Delivery within 14 days occurred in 15.5% of women with CL ≤ 14 mm versus 7.3% of those with longer cervices, and CL ≤ 14 mm remained independently associated with the outcome after adjustment (adjusted odds ratio 2.62; 95% CI 1.59–4.27; P < 0.001). Conclusion In singleton pregnancies with a newly diagnosed short cervix at 24 0/7 –33 6/7 weeks, a CL of ≤ 14 mm is independently associated with delivery within 14 days, although discrimination is modest. The threshold might have greater value when combined with symptoms, gestational age, and other clinical factors.