Abstract: Objective：To evaluate the suitable time and dosage of mifepristone and misoprostol forthe cervical priming prior to vacuum aspiration. Methods：This is a randomized and double blind clinical trial. 900 cases of pregnant woman who wasprimi-gravid or had only once early abortion were randomly divided into four groups.100 mg of mifepristone were given at 12h（groupA）or 36h（groupB）pre-operation. 0.6 mg（groupC）or 0.4 mg（groupD）of misoprostol were given at 3h pre-operation. Effects of mifepristone and misoprostol on cervical primingwere compared. Results：The effective rates of cervical dilatation of mifepristone in group A and group B were 65.73% and 77.10%（P=0.01）, while the mean values of cervical dilatation were（6.21依1.08）mm and（6.66依1.17）mm, respectively（P约0.01）. The difference was insignificant when compared those results between people being primi-gravida or not, or compared people under anesthesia or not. The effective rates of cervical dilatation of misoprostol ingroup C and group D were 75.1% and 70.3%（P=0.261）, while the mean values of ervical dilatation were（6.64依1.15） mm and（6.41依1.15）mm, respectively（P=0.04）. Effect of misoprostol in primi-gravida women was identified with that of overall people. Conclusions：100 mg of mifepristone at 36h pre-operation or 0.6 mg of misoprostol at 3hpre-operation was suitable for the cervical priming prior to vacuum aspiration, and misoprostol was more practical.

Key words: Pregnancy, first trimester, Abortion, induced, Misoprostol, Mifepristone, Cervix uteri, Case-control studies