Induction of labour: clinical predictive factors for success and failure.

Induction of labour (IOL) is a widely-used practice in obstetrics. Our aim was to evaluate predictors of vaginal delivery in postdate pregnancies induced with prostaglandins. We conducted a retrospective cross-sectional study with analytic component. A total of 145 women, admitted for IOL after the 41st week of gestation, were induced with a vaginal pessary releasing prostaglandins. Type of delivery, whether vaginal or caesarean, was the outcome. Several maternal and foetal variables were investigated. The Kaplan-Maier curves, monovariate and a multivariate logistic regression were carried out. In our population, 80.7% of women had vaginal delivery after the induction. Multiparity and a high Bishop score at the beginning of the IOL were protective factors for a vaginal delivery (respectively OR 0.16, p = .028 and OR 0.62, p = .034) while age >35 years, and the foetal birth weight >3500 g at the birth, resulted in being risk factors for caesarean section (respectively OR 4.20, p = .006 and OR 3.63, p = .013). IMPACT STATEMENT What is already known on this subject: Induction of labour (IOL) is a widely used practice in obstetrics. Scientific literature shows several predictors of successful induction, although there is no unanimity except for 'multiparity' and 'favourable Bishop score' which are associated with positive outcome of the induction. The main difficulty in finding other predictive factors is the heterogeneity of this field (different local protocols in each hospital, type of induction, populations and outcomes chosen in each study). In addition to that, populations are not always comparable due to the different gestation. For this reason, we decided to select a specific population of women, such as low risk postterm pregnancies induced with prostaglandins, in order to detect possible predictive factors for the success of the IOL for women with uncomplicated pregnancies. What the results of this study add: Our study agrees with existing literature that 'multiparity' and 'Bishop score' are linked with the success of IOL and adds that 'maternal age' and 'foetal birth weight' are significant risk factors for the population of uncomplicated post term pregnancies induced with prostaglandins. What the implications are of these findings for clinical practice and/or further research: Our results agreed with the existing literature regarding parity and Bishop score but not for maternal age and birth weight. This adds new precious data to the literature which could be used for systematic reviews and for implementing IOL guidelines and protocols, nationally and internationally. Our findings could be also used for guiding future research in this field. It will be interesting to investigate the existence of not just specific factors but also any combination of variables which could predict the success of the procedure. At the moment these information cannot be used in terms of decision making for healthcare professionals as no variable is 100% predictive but once further research will be added, we may be able to know when is best time to start the IOL, how to facilitate the success of the procedure and how to best support the woman throughout the whole experience.