Ultrasound prediction of the outcome of labor induction: which is the role of the cervical sliding sign?

Objectives Pre-induction cervical status is the most important predictor of successful induction of labor (IOL) and has been traditionally assessed by the Bishop Score. However, it has been shown to be subjective, with poor reproducibility a high intra- and interobserver disagreement, and a poor predictor for the outcome of IOL at term. Therefore, we have conducted a prospective observational cohort study in order to evaluate the role of the cervical sliding sign (CSS) in the prediction of successful vaginal delivery after induction of labor in women with an unfavorable cervix.

Methods Multicenter prospective study involving a non-consecutive series of uncomplicated singleton term pregnancies, planned for induction of labor (IOL), with a fetus in cephalic presentation and unfavorable cervix (Bishop score≤6). We evaluated the Bishop score by digital examination and the cervical length and CSS by transvaginal ultrasound. The CSS was defined as the sliding of the anterior cervical lip on the posterior one under gentle pressure of the transvaginal probe. The main outcomes of the study were the induction-to-active-labor time and successful vaginal delivery within 24 hours. Secondary outcomes were time to delivery (TtD) and active-labor-to-delivery time. Women who had cesarean delivery for fetal distress or reasons other than failure to progress in labor were excluded from final analysis.

Results Over a period of 8 months, 180 patients were included, of whom 111 (65%) were nulliparae. The CSS was present in 42 nulliparae (39%) and in 38 (64%) parous women. A shorter cervix was noted in patients with a positive CSS (21.8±7.0 vs. 31.1±7.8 mm, p=0,001). In the nulliparous group, the presence of CSS was significantly associated with an increased likelihood of vaginal delivery<24h (52.4 vs. 24.6%, p<0.01), a shorter induction-to-active-labor time (20.1±10.8 vs. 30±10.7 hours, p<0.01) and TtD (24.9±12.1 vs. 30±10.7, p=0,01).In the multiparous group, the presence of CSS was significantly associated with a higher likelihood of vaginal delviery<24h (86,8 vs. 54.5%, p=0,01), a shorter induction-to-active-labor time (11±7.6 vs. 16.7±9.1 hours, p<0.01) and TtD (13.8±8.7 vs. 19.6±9.6 hours, p<0,001). The CSS was independently associated with TtD (p=0,012) and vaginal delivery<24h (p=0,001) in the overall study population at linear and logistic regression analysis, respectively. The CSS was also independently associated with vaginal delivery<24h in nulliparous and parous women (p=0,011, p=0,031).

Conclusion In women undergoing IOL with an unfavorable cervix, a positive CSS does seem to be associated with a shorter induction-to-active-labor time and a higher probability of vaginal delivery<24h. Introduction of this marker into new prediction models should be addressed in future studies to further improve its predictive value.

Publication History

Article published online:
26 November 2021