Effect of vaginal pH on the efficacy of vaginal misoprostol for induction of midtrimester abortion

Aim: To evaluate the effect of vaginal pH on the efficacy of misoprostol for induction of midtrimester abortion. Methods: The study comprised 110 women, with a gestational age of 14-26 weeks, with a missed abortion as an indication for the induction of abortion. On admission, the vaginal pH was measured and two groups were generated: (A) those with pH < 5 (n = 63); and (B) those with pH ≥ 5 (n = 47). All of the women received intravaginal misoprostol tablets moistened with 3 mL of 5% acetic acid, 200 μg every 4 h for a maximum of 5 doses within 24 h. If the patient did not have adequate uterine contractions, the same regimen was repeated over the following 24 h and if no response was achieved, this was considered a failure of therapy. Results: All patients aborted within 48 h. A significant positive correlation between vaginal pH and the misoprostol application-abortion interval was found. The mean induction-abortion interval was significantly shorter in group A compared to group B (12.1 vs 23.6 h, P < 0.001), with abortion rates at 24 h being 100% and 63.8%, respectively. Moreover, a significantly lower dose of misoprostol was used in group A with a lower incidence of fever and abdominal pain. Conclusion: Vaginal pH influences the efficacy of misoprostol administered vaginally for the induction of midtrimester abortion. The presence of this relationship, despite premoistening misoprostol with an acidifying agent, suggests that the effect of vaginal pH might extend beyond affecting the pharmacokinetics of the drug. © 2007 The Authors.