Effect of vaginal pH on efficacy of the dinoprostone gel for cervical ripening/labor induction

OBJECTIVE: The purpose of this study was to evaluate whether vaginal pH has an effect on the efficacy of the dinoprostone gel for cervical ripening/labor induction. STUDY DESIGN: Thirty-two women with an unfavorable cervix who were undergoing labor induction were enrolled in this prospective, double-blinded investigation. Initial vaginal pH and Bishop score assessment were made by an independent examiner. All women received cervical ripening with the dinoprostone gel 5 mg intracervically, with repeated dosing one time 6 hours later. Twelve hours later, oxytocin induction was initiated per standardized protocol, and outcome data were collected. RESULTS: Mean (±SD) initial vaginal pH was 4.7 ± 0.6 (range, 4.0-6.0) for the study cohort. No significant differences were noted between women with a high vaginal pH (>4.5, n = 16 women) and women with a low vaginal pH (≤4.5, n = 16 women) with respect to maternal age, parity, gestational age, or initial Bishop score. Although Bishop score change over the initial 12 hours of cervical ripening did not significantly differ between the high vaginal pH (2.3 ± 2.3) and the low vaginal pH group (2.3 ± 2.5, P = not significant), time to active labor (19 ± 10 hours vs 33 ± 17 hours, P = .001), complete dilation (24 ± 10 hours vs 37 ± 19 hours, P = .03), and delivery (26 ± 10 hours vs 38 ± 18 hours, P = .02) were significantly shorter in women with a high vaginal pH compared with women with a low vaginal pH, respectively. A significant association was noted between vaginal pH and time to active labor (r = -0.52, P = .003), complete dilation (r = -0.50, P = .006), and delivery (r = -0.44, P =.01); however, pH was not significantly associated with Bishop score change during the initial 12 hours of cervical ripening. CONCLUSION: Vaginal pH is an important factor that affects the efficacy of the dinoprostone gel as an adjuvant for labor induction.