Pregnancy: The effect of dose of mifepristone and gestation on the efficacy of medical abortion with mifepristone and misoprostol

Although it has been demonstrated that a combination of mifepristone and a prostaglandin is an effective method of inducing abortion in early pregnancy, the optimum dose of the antigestogen is unknown. Women (n = 220) requesting abortion in early pregnancy (< or = 63 days amenorrhoea) were randomized to receive a single dose of either 600 or 200 mg mifepristone followed 48 h later by a single dose of 600 micrograms misoprostol by mouth. The percentage of women who had a complete abortion (93.6% confidence interval 90.4-95.5%) was identical in the two groups. There was no significant difference in the number of women who passed the fetus within 4 h of receiving the prostaglandin (64 versus 74%), the days of bleeding (14.6 +/- 1.1 versus 15.3 +/- 0.9) nor in the onset of the next period (39.7 +/- 1.3 versus 36.7 +/- 1.3) respectively between the groups receiving 200 or 600 mg mifepristone. However, the complete abortion rate was significantly higher in women < or = 49 days compared to women 50-63 days amenorrhoea (97.5 versus 89.1% respectively; P < 0.02). There was no difference in any of the other parameters at different weeks of gestation. We conclude: (i) that the recommended dose of mifepristone could be reduced from 600 to 200 mg without loss of clinical efficacy, (ii) that the combination of mifepristone and 600 micrograms misoprostol is a highly effective alternative to vacuum aspiration for inducing abortion in women < 50 days amenorrhoea and (iii) at gestation > 56 days, this combination may result in too many incomplete abortions to be clinically acceptable.