Methods for assessing pre‐induction cervical ripening

BACKGROUND: Induction of labour is the artificial initiation of labour in a pregnant woman after the age of fetal viability but without any objective evidence of active phase labour and with intact fetal membranes. The need for induction of labour may arise due to a problem in the mother, her fetus or both, and the procedure may be carried out at or before term. Obstetricians have long known that for this to be successful, it is important that the uterine cervix (the neck of the womb) has favourable characteristics in terms of readiness to go into the labour state. OBJECTIVES: To compare Bishop score with any other method for assessing pre‐induction cervical ripening in women admitted for induction of labour. SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 March 2015) and reference lists of retrieved studies to identify randomised controlled trials (RCTs). SELECTION CRITERIA: All RCTs comparing Bishop score with any other methods of pre‐induction cervical assessment in women admitted for induction of labour. Cluster‐RCTs were eligible for inclusion but none were identified. Quasi‐RCTs and studies using a cross‐over design were not eligible for inclusion. Studies published in abstract form were eligible for inclusion if they provided sufficient information. Comparisons could include the following. 1. Bishop score versus transvaginal ultrasound (TVUS). 2. Bishop score versus Insulin‐like growth factor binding protein‐1 (IGFBP‐1). 3. Bishop score versus vaginal fetal fibronectin (fFN). However, we only identified data for a comparison of Bishop score versus TVUS. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed the trials for inclusion, extracted the data and assessed trial quality. Data were checked for accuracy. MAIN RESULTS: We included two trials that recruited a total of 234 women. The overall risk of bias was low for the two studies. Both studies compared Bishop score withTVUS. The two included studies did not show any clear difference between the Bishop score and TVUS groups for the following main outcomes: vaginal birth (RR 1.07, 95% CI 0.92 to 1.25, moderate quality evidence), caesarean delivery (RR 0.81, 95% CI 0.49 to 1.34, moderate quality evidence), neonatal admission into neonatal intensive care unit (RR 1.67, 95% CI 0.41 to 6.71, moderate quality evidence). Both studies only provided median data in relation to induction‐delivery interval and reported no clear difference between the Bishop and TVUS groups. Perinatal mortality was not reported in the included studies. For the review's secondary outcomes, the need for misoprostol for cervical ripening was more frequent in the TVUS group compared to the Bishop score group (RR 0.52, 95% CI 0.41 to 0.66, two studies, 234 women, moderate quality evidence). In contrast, there were no clear differences between the Bishop scope and TVUS groups in terms of meconium staining of the amniotic fluid, fetal heart rate abnormality in labour, and Apgar score less than seven. Only one trial reported median data on the induction‐delivery interval and induction to active phase interval, the trialist reported no difference between the Bishop group and the TVUS group for this outcome. Neither of the included studies reported on uterine rupture. AUTHORS' CONCLUSIONS: Moderate quality evidence from two small RCTs involving 234 women that compared two different methods for assessing pre‐induction cervical ripening (Bishop score and TVUS) did not demonstrate superiority of one method over the other in terms of the main outcomes assessed in this review. We did not identify any data relating to perinatal mortality. Whilst use of TVUS was associated with an increased need for misoprostol for cervical ripening, both methods could be complementary. The choice of a particular method of assessing pre‐induction cervical ripening may differ depending on the environment and need where one is practicing since some methods (i.e. TVUS) may not be readily available and affordable in resource‐poor settings where the sequelae of labour and its management is prevalent. The evidence in this review is based on two studies that enrolled a small number of women and there is insufficient evidence to support the use of TVUS over the standard digital vaginal assessment in pre‐induction cervical ripening. Further adequately powered RCTs involving TVUS and the Bishop score and including other methods of pre‐induction cervical ripening assessment are warranted. Such studies need to address uterine rupture, perinatal mortality, optimal cut‐off value of the cervical length and Bishop score to classify women as having favourable or unfavourable cervices and cost should be included as an outcome.