Vaginal misoprostol for pre-abortion cervical priming: is there an optimal evacuation time interval?

To determine the optimal evacuation time interval in the use of vaginal misoprostol for cervical priming before first trimester termination of pregnancy.

Prospective double-blind randomised study.

Fertility Control Centre, National University Hospital, Singapore.

Sixty healthy nulliparous women requesting legal termination of pregnancy between 6 and 11 weeks of gestation were randomly allocated to either the 400 microg or 600 microg misoprostol group. Vacuum aspiration was performed after three hours in the 400 microg group and at the end of two hours in the women given 600 microg misoprostol. Using Hegar's dilator, degree of cervical dilatation before operation was measured. Other parameters assessed included the amount of additional dilatation required (if < Hegar 8), pre-operative and intra-operative blood loss, and associated side effects.

For the 600 microg group, only five women (16.7%) achieved a cervical dilatation of > or = 8 mm, compared with 28 women (93.3%) in the 400 microg group. Using the 400 microg misoprostol group as a baseline, the odds ratio was 0.014 (95% CI 0.003-0.080) for 600 microg for successful pre-operative cervical dilatation of > or = 8 mm. The mean cervical dilatation for 400 and 600 microg misoprostol was 8.1 mm and 6.6 mm, respectively (P < 0.001). Despite the shorter evacuation time interval of two hours, the 600 microg dose was associated with an increase in side effects such as vaginal bleeding, abdominal pain and a fever of > 38.0 degrees C. However, other than abdominal pain, no significant differences in the frequency of these side effects were shown.

Use of 400 microg misoprostol with a minimal evacuation time interval of three hours still appears the optimal dosage and evacuation time for cervical priming before first trimester termination of pregnancy.