[Transvaginal ultrasound assessment of the cervix and digital examination before labor induction]

Abstract

Objective: To examine the relationship between sonographic measurement of cervical length and Bishop score with duration of labour induction.

Methods: A prospective, blinded, observational study was performed in 191 pregnant women undergoing labor induction. Ultrasound measurement of cervical length and determination of Bishop score were performed. Induction was based exclusively on the Bishop score according to Obstetric Unit protocol. The criteria for considering the cervix unripe were either Bishop score < 6 or a cervical length = 26 mm. Duration of induction is defined like the induction-to-delivery interval. The main outcomes assessed were the duration of induction, the delivery within 24 h of induction and type of delivery.

Results: The duration of induction was between 2 h 27 min and 61 h 30 min. We found an association between cervical length and Bishop score with duration of induction. The duration of induction was significantly increased in nulliparous (median 18 h 38 min vs. 9 h 18 min). There was no correlation of age or weight of pregnant women with the duration of induction. Comparison between Bishop score and cervical length in predicting delivery within the first 24 hours showed that the pregnant women with low Bishop score had a higher risk of deliver after 24 hours of induction (OR = 21.16), as the ones with cervical length longer than 26 mm (OR = 5.06). Analyzing the relation of these two parameters with type of delivery we realize that low Bishop score has a higher risk of cesarean section (OR = 2.67) and that there wasn't any relation between type of delivery and cervical length.

Discussion: In this study we verified a statistically significant relation between Bishop score, US cervical length and previous vaginal birth with induction duration. Pregnant woman's age and weight didn't have influence on the duration of induction. The study showed that both Bishop score and US cervical length are useful in predicting delivery within the first 24 hours. Bishop score was also related with type of delivery.