Ultrasound Measurement of Cervical Length at 36-36+6 Weeks' Gestational Age to Predict Spontaneous Onset of Labor and Mode of Delivery.

Background and objective Cesarean section rates are rising globally, including in India. Following the ARRIVE trial, elective induction at 39 weeks has become more common. Cervical length is included in the Bishop score for assessing cervical favorability; however, the Bishop score is subjective and has limited predictive value. This study proposes that an objective third-trimester transvaginal ultrasound measurement of cervical length at 36 weeks may better predict spontaneous labor onset and guide delivery management. The objective of this study is to determine the correlation between cervical length at 36-36+6 weeks and spontaneous labor onset and to assess its effectiveness in predicting mode of delivery. Methods This prospective observational study included 95 eligible pregnant women at a tertiary hospital over 18 months. All underwent transvaginal cervical length measurement between 36 and 36+6 weeks. Demographic and obstetric data (including Bishop score) were collected, and participants were followed until delivery. Outcomes were spontaneous labor by 39 weeks and the mode of delivery. Data were analyzed using chi-square tests for categorical variables and Pearson's correlation for continuous variables, with significance at p < 0.05. Results Cervical length at 36-36+6 weeks showed no significant correlation with spontaneous labor by 39 weeks; all 95 women required induction. Longer cervical lengths were significantly associated with prolonged induction-to-delivery intervals (r = 0.491). Women with longer cervices more often required Foley catheter ripening (p = 0.001), while none with very short cervices (≤2.5 cm) required emergency cesarean delivery. Cervical length was not associated with gestational age at delivery (p = 0.065). These findings align with evidence that shorter cervical lengths predict faster inductions and higher vaginal delivery rates, whereas longer cervices are linked to the need for multiple induction methods and increased cesarean likelihood. Conclusions Cervical length measurement at 36-36+6 weeks can inform induction strategies at term. Although not predictive of spontaneous labor onset, longer cervical length was associated with prolonged induction, greater need for mechanical ripening, and higher cesarean risk. These results support incorporating cervical length assessment into preinduction evaluation. Identifying a longer cervix at 36 weeks can alert clinicians to the likely need for intensive induction methods (e.g., Foley catheter) and the potential for cesarean delivery if the cervix remains unfavorable. The findings align with guidelines advocating individualized induction based on objective cervical assessment. Combining the Bishop score with sonographic cervical length at 36-37 weeks may improve the prediction of induction success and guide delivery planning. Further research should refine how cervical length measurement can be integrated into standard induction protocols to improve maternal and neonatal outcomes.