Patients with an ultrasonographic cervical length ≤15 mm have nearly a 50% risk of early spontaneous preterm delivery

OBJECTIVE: The aim of this study was to determine the value in the prediction of spontaneous preterm delivery of ultrasonographically measured cervical length measured between 14 and 24 weeks' gestation. STUDY DESIGN: A retrospective cohort study examined cervical length by means of a two-stage procedure, transabdominal ultrasonography followed by transvaginal ultrasonography ii cervical length was <30 mm. RESULTS: A total of 6877 patients met inclusion criteria. Mean cervical length was 37.5 mm. Odds ratios for early preterm delivery (less than or equal to 32 weeks' gestation) for patients with cervical lengths less than or equal to 10, less than or equal to 15, less than or equal to 20, less than or equal to 25, and less than or equal to 30 mm were, respectively, 29.3 (95% confidence interval, 11.3-75.8), 24.3 (95% confidence interval, 12.9-45.9), 18.3 (95% confidence interval, 10.8-31.0), 13.4 (95% confidence interval, 8.8-20.6), and 3.2 (95% confidence interval, 2.4-4.4). For early preterm delivery a cervical length of less than or equal to 15 mm had a positive predictive value of 47.6%, a negative predictive value of 96.7%, a sensitivity of 8.2%, and a specificity of 99.7%. CONCLUSIONS: A short cervix seen on a second-trimester sonogram was a powerful predictor of early spontaneous preterm delivery (less than or equal to 32 weeks' gestation). Nearly 50% of patients with a cervical length less than or equal to 15 mm had an early spontaneous preterm delivery, which suggests that clinical trials of interventions (eg, cerclage) in this population are urgently needed.