Ultrasound-Assessed Cervical Volume as a Predictor of Labor Induction Success in Late Preterm and Term Pregnancies With an Unfavorable Cervix.

OBJECTIVE

To evaluate the predictive value of ultrasound-assessed cervical volume for successful labor induction in late preterm and term pregnancies with an unfavorable cervix and to compare its performance with cervical length.

METHODS

This prospective study included 350 singleton pregnancies at ≥ 34 weeks of gestation undergoing labor induction with an unfavorable cervix. Cervical length and cervical volume were measured by transvaginal ultrasound prior to induction, with cervical volume calculated using a cylindrical geometric model. Successful induction was defined as vaginal delivery within 24 h. Receiver operating characteristic curve analysis and multivariable logistic regression were performed to assess predictive performance and identify independent predictors after adjustment for maternal age, body mass index, parity, and gestational age.

RESULTS

Labor induction was successful in 222 patients (63.4%). The successful induction group had significantly higher Bishop scores, shorter cervical lengths, and smaller cervical volumes (all p < 0.001). Cervical volume showed a positive correlation with cervical length and a negative correlation with Bishop score. Cervical length ≤ 33 mm (AUC = 0.836) and cervical volume ≤ 29.8 cm3 (AUC = 0.798) predicted induction success, with comparable predictive performance. Both cervical length (aOR = 0.78, 95% CI: 0.73-0.84) and cervical volume (aOR = 0.93, 95% CI: 0.90-0.97) were independent predictors of successful induction, while multiparity was a strong positive predictor. Similar findings were observed in term and late preterm subgroups.

CONCLUSION

Cervical volume is an independent predictor of labor induction success in late preterm and term pregnancies with an unfavorable cervix and demonstrates predictive performance comparable to cervical length.