The Effect of Vaginal pH on the Efficacy of Vaginal Misoprostol for the Induction of Midtrimester Pregnancy Termination

Vaginal misoprostol is said to dissolve better in an acidic environment, thus, in this study we aimed to evaluate the influence of increasing vaginal acidity on the effectiveness of vaginal misoprostol for the induction of midtrimester pregnancy using acidic environment.

A total of 40 women requiring second trimester pregnancy termination were randomly assigned to one of two treatment groups: (A) in the saline group, 400 µg of intra-vaginal misoprostol was moistened in normal saline before the vaginal insertion as controls (n = 20); and (B) in the acetic acid group, the acidity of the vagina was increased with 3% of acetic acid, (4 mL of 3% acetic acid was delivered into the vagina every 6 hours) before the insertion of an initial dose of 400 µg misoprostol (n = 20). Then 200 µg dosage was repeated every 4 hours for a maximum of 5 doses within 24 hours. If the patient did not have adequate uterine contractions, the same regimen was repeated over the following 24 hours and if no response was achieved, this was considered a failure of therapy.

There was no significant difference in the vaginal pH between the control and intervention groups before the vaginal application of acetic acid (5.80 ± 0.62 versus 5.89 ± 0.49, P = 0.622,). The vaginal pH was significantly lower in the acetic acid group after the vaginal application of acetic acid compared to the control group (5.11 ± 0.56 versus 5.80 ± 0.62, P = 0.001). Overall, 95% of pregnancies were successfully terminated in the acetic acid group compared to 85% in the control group. These differences were not statistically significant (P =0.241). The success rate within 24 hours and 48 hours, the adverse effects, mean termination time, total misoprostol administered, and the number of curettage were, also, comparable between the two groups.

Findings from this study shows that increasing Vaginal acidity does not improve the efficacy of misoprostol administered intra-vaginally for the second trimester pregnancy termination.