A Predictive Model For the Outcome of Induction of Labor in Term Nulliparous Women

Background: Induction of labor is artificial stimulation of uterine contractions before the spontaneous onset of labor, with the aim of achieving vaginal delivery. Induction of labor can fail in certain patients, which can lead to several sequelae including emergency cesarean section. Several maternal and fetal characteristics are associated with increased risk of failed induction, but a universally accepted criterion is not yet available.Objective: To detect antepartum factor associated with increased risk of failed induction of labor in term nulliparous women and create a model to calculate the overall risk.Study Design: This was a retrospective cohort study conducted in Yas hospital, Tehran, Iran from 2015 until 2017. A total of 700 term nulliparous women with singleton pregnancy of more than 37 weeks were included in this study. Patients with non-cephalic presentation, placenta previa, preeclampsia, diabetes, prolonged premature rupture of membranes, previous myomectomy and patients undergoing spontaneous labor were excluded from the study. Maternal and fetal characteristics were assessed. Patients underwent induction of labor using different methods. Patients with failed induction underwent emergency cesarean section. Univariate and multivariate logistic regression was used to detect factors contributing to failed induction.Results: 400 patients (57.14%) had vaginal delivery and 300 patients (42.86%) had emergency cesarean section. Cesarean section was done due to: arrest of descent or full arrest (19.66%), arrest of latent phase (9.33%) and arrest of dilation (71%). In univariate analysis, higher maternal age, higher weight, higher BMI, higher duration of latent and active phase of labor, lower gestational age, lower cervical dilation and effacement, lower fetal station, lower Bishop score and fetal head positions other than occipitoanterior were associated with increased risk of failed induction. In multivariate analysis, Increased maternal age (OR=1.05, CI: 1.00-1.09, P=0.028), decreased maternal height (OR=0.95, CI: 0.90-0.99, P=0.043), increased maternal BMI (OR=1.09, CI: 1.01-1.17, P=0.024), increased gestational age (OR=1.61, CI:1.3-2.0, P=0.000), lower fetal station (OR= 0.48, CI: 0.24-0.96, P=0.039), decreased Bishop score (OR=0.48, CI: 0.27-0.71, P=0.001), longer latent phase (OR=1.65, CI: 1.47-1.85, P=0.000) and longer active phase (OR=2.60, CI: 2.20-3.09, P=0.000) were associated with higher risk of failed induction.Conclusions: We showed that that higher maternal age, lower maternal height, higher maternal BMI, higher gestational age, lower fetal station, lower modified Bishop score, longer latent and active phase are associated with an increased risk of failed induction of labor in term nulliparous women. We also created a model to predict the risk of failed induction in these women.

Keywords:

induction of labor , failed induction , predictive model , Bishop score , nulliparous , cesarean.