ObjectiveTo compare cervical dilation and the Bishop score as correlates of successful labor induction and vaginal delivery and to determine whether the prognosis of postripening cervical characteristics varies with the method of ripening used.MethodsFour hundred forty-three women with Bishop scores less than 9 who required induction of labor were assigned randomly to cervical ripening with prostaglandin E2 gel or hygroscopic dilation. The Bishop score and its component characteristics were evaluated as univariate correlates of successful induction of labor and vaginal delivery and then were assessed using logistic regression to adjust for other maternal and fetal factors. The differences in the association between method of ripening and successful labor induction were evaluated relative to pre-ripening and post-ripening cervical examination characteristics.ResultsCervical dilation was a better correlate of successful labor induction and vaginal delivery than was the Bishop score, even after exclusion of patients with initial Bishop scores greater than 6 and dilation greater than 3.0. Both ripening methods yielded similar success in labor induction and vaginal delivery, but when categorized by post-ripening cervical examinations, patients undergoing hygroscopic ripening had lower rates of successful labor induction and vaginal delivery.ConclusionCervical dilation is a better predictor of successful labor induction and vaginal delivery than either the Bishop score or any other Bishop score component characteristic. The likelihood of successful labor induction and vaginal delivery based on post-ripening cervical characteristics varies by the ripening method used.