Sonographic Cervical Length Measurement before Labor Induction in Term Nulliparous Women

Abstract

Objective: The purpose of the study was to determine if transvaginal sonographic measurement of the cervical length is a useful method to predict successful labor induction in nulliparas. Methods: 137 women who were scheduled for medically indicated induction of labor had a transvaginal sonographic measurement of the cervical length before labor induction. Inclusion criteria were: (1) singleton pregnancy; (2) gestational age between 37–42 weeks; (3) live fetus in cephalic presentation; (4) intact membranes; (5) no vaginal bleeding; (6) no previous history of uterine surgery; (7) nulliparous women, and (8) no allergy or asthma in response to prostaglandins. Induction of labor was performed within 6 h of the ultrasonographic examination, by inserting 2 mg of dinoprostone in the posterior vaginal fornix, repeated if needed every 6 h for up to three doses. When the cervix became favorable and no regular contractions were observed, amniotomy and oxytocin augmentation, starting at 1 mIU/min and increasing 1 mIU every 30 min as necessary, was performed. Results: All women were Caucasians and the mean age was 24.3 years (range 19–37 years). The mean cervical length was 28 mm (range 11–39 mm). The Bishop score was ≤5 in 101 women and >5 in the 36 others. Vaginal delivery occurred in 92 women (67.1%), and the vast majority of them (89 women; 96.7%) gave birth within 24 h of induction. Forty-five women (32.8%) had a cesarean section. The Bishop score was not predictive of the mode of delivery. Thirty-six of 101 women (35.6%) with a Bishop score ≤5 delivered by cesarean section, compared to 9 of 36 women with a Bishop score >5 (25%) (p = NS). Women with a cervical length <27 mm were more likely to deliver vaginally. Using this cutoff value the sensitivity of a successful labor induction was 76% and the specificity was 75.5%. Conclusions: Transvaginal sonographic measurement of cervical length is a good predictor of a successful labor induction at term in nulliparas.