Preinduction sonographic measurement of cervical length in post-term nulliparous women with low cervical score: A pilot study

Objectives: To assess the value of preinduction sonographically measured cervical length in a group of post-term nulliparous women with low Bishop score, for the prediction of failure of labour induction. Methods: The pilot project was conducted prospectively in a selected group of 43 primiparous women, scheduled for induction because of prolonged pregnancy (41 completed weeks), with Bishop score ≤ 4. Pre-induction cervical length was sonographically measured upon recruitment. Four patients were excluded from the study due to spontaneous onset of labour. Patients were divided into two groups according to the mode of delivery and were individually matched by demographic variables. The cervical length was assessed in the two groups, and two Receiver-Operating Characteristic curves were calculated to determine the best threshold values of cervical length for the prediction of the time to onset of labour and of delivery. The likelihood of successful induction was assessed using Kaplan-Meier survival curves and the risk of caesarean section by χ2. Results: Eighteen women (46%) had a caesarean section where failure of induction was the main indication (50%). The cervical length was longer in the group of patients with caesarean section (p = 0.03), although there was no correlation between the cervical length and onset of active labour. A cervical length < 26 mm showed the best predictive value for delivery within 24 hours (sensitivity 66.7%, specificity 91.3%). A positive association between cervical length and risk of caesarean delivery was reported. Conclusion: Transvaginal sonographic assessment of the cervical length before induction of labour, in post-term nulliparous women with unfavourable cervix, seems to have the potential to identify those at high risk of caesarean section.