A comparative study using two dose regimens (200 μg or 400 μg) of vaginal misoprostol for pre-operative cervical dilatation in first trimester nulliparae

Objective To determine the optimal dosage and dosing interval for the use of misoprostol administered vaginally for pre-operative cervical dilatation. Design Prospective double-blind randomised study. Setting Fertility Control Centre, National University Hospital, Singapore. Methods Women were randomly allocated to either the 200 mu g or the 400 mu g misoprostol group. Vacuum aspiration was performed at either three or four hours after the insertion of misoprostol tablets. Using Hegar's dilatator, degree of cervical dilatation before operation was measured. Other parameters assessed included the amount of additional dilatation required (if it was < Hegar 8), pre-operative and intra-operative blood loss, and associated side effects. Results For the 200 mu g misoprostol group, only seven (23.3%) achieved a dilatation of greater than or equal to 8 mm compared with 29 women (96.7%) in the 400 mu g misoprostol group. The odds ratio was 95.3 (95% CI 10.9-830.9) for 400 mu g misoprostol for successful pre-operative cervical dilatation of greater than or equal to 8 mm. The mean cervical dilatation for 400 mu g and 200 mu g misoprostol was 8.2 mm and 6.4 mm, respectively (P < 0.001). The use of 400 mu g misoprostol with an evacuation interval of three hours appears to be the optimal dosage and evacuation time interval. Increasing the time interval beyond three hours did not confer any additional advantage on the rate of successful cervical dilatation but was instead associated with an increase in side effects such as vaginal bleeding, lower abdominal pain and the appearance of products of conception at the cervical os. However, besides vaginal bleeding, no significant differences in the frequency of these side effects were demonstrated. Conclusion This first report on the comparison of differing dosages and time intervals to determine the optimal dosage treatment schedule shows that the vaginal application of 400 mu g misoprostol for at least three hours is optimal for pre-operative cervical dilatation before vacuum aspiration in first trimester nulliparae.