Effect of vaginal pH on efficacy of the controlled-release dinoprostone vaginal insert for cervical ripening/labor induction

Objective: To evaluate whether vaginal pH alters the efficacy of the controlled-release dinoprostone vaginal insert (Cervidil®) for cervical ripening/labor induction. Methods: Thirty-four women with an unfavorable cervix undergoing labor induction were enrolled in this prospective, double-blind investigation. Vaginal pH and Bishop score assessments were made by an independent examiner. All women received preinduction with the dinoprostone vaginal insert 10 mg intravaginally for 12 h. Twelve hours later, oxytocin induction initiated according to the standardized protocol and outcome data were collected. Results: Mean (± SD) initial vaginal pH was 4.9 ± 0.5 for the study cohort. No significant differences were noted between women with a high vaginal pH (> 4.5, n = 18) and those with a low vaginal pH (≤ 4.5, n = 16) with respect to maternal age, parity, gestational age, or initial Bishop score. Similarly, Bishop score change over the preinduction interval (3.2 vs. 3.3), time to active labor (28.6 vs. 24.6 h) and time to delivery (33.7 vs. 31.4 h) were not significantly different between the low and the high pH groups, respectively. Linear regression analysis revealed no significant association between vaginal pH and Bishop score change during the preinduction interval, time to active labor, time to complete dilatation, or time to delivery. Conclusion: Vaginal pH does not appear to influence the efficacy of the controlled-released dinoprostone vaginal insert for cervical ripening/labor induction.