Factors affecting the likelihood of successful induction after intravaginal misoprostol application for cervical ripening and labor induction

OBJECTIVE: Our purpose was to determine whether maternal age, height and weight, parity, duration of pregnancy, cervical dilatation or Bishop score, and birth weight could be used to predict the likelihood of successful induction in women given intravaginal misoprostol. STUDY DESIGN: A computerized database was compiled of 1373 pregnancies in which intravaginal misoprostol was given for cervical ripening and labor induction. Most of these women were placed on investigational protocols in which the dose of misoprostol administered was 25 to 50 microg and the dosing intervals ranged from 3 to 6 hours. No more than 24 hours of administration was permitted. Induction was undertaken in women with unfavorable cervical examinations (Bishop scores of 4 or less) and without spontaneous labor or ruptured membranes. Univariate and stepwise multiple regression analyses were performed to identify those factors associated with successful induction, defined as vaginal delivery within 24 hours of induction. RESULTS: Six hundred fifty-seven (48%) had successful induction. Parity (odds ratio [OR] 2.5, 95% CI 2.0-2.9, P <.0001), initial cervical dilatation (OR 1.9, 95% CI 1.6-2.3, P <.0001), Bishop score (OR 1.6, 95% CI 1.3, 1.8, P <.0001), and gestational age at entry (OR 1.3, 95% CI 1.1-1.5, P =.002) were significant at the.05 level for predicting successful induction. A multivariate stepwise logistic regression was then performed to evaluate each of these as independent predictors. Parity (OR 2.4, 95% CI 2.0-3.0, P <.0001), initial cervical dilatation (OR 1.7, 95% CI 1.4-2.1, P <.0001), and estimated gestational age (OR 1.3, 95% CI 1.1-1.6, P =.003) are significant independent predictors for successful induction, but initial Bishop score is not significant (P =.19) after adjustment for other significant predicting factors. CONCLUSIONS: The clinical characteristics of parity, initial cervical dilatation, and gestational age at entry are predictors of the likelihood of success of cervical ripening and labor induction with intravaginal misoprostol administration.