Cervical ripening with mifepristone (RU 486) in first trimester abortion. An electron microscope study

Mifepristone (RU 486) is a steroid that binds to the progesterone receptor and acts as a progesterone antagonist. It has been used clinically to terminate an early pregnancy. In the present investigation, the effects of mifepristone on the fine structure of the cervix were evaluated in two groups of women undergoing a first trimester abortion, using a triple-blind randomized protocol. In group I (n = 18), a cervical biopsy was taken after two doses of 100 mg mifepristone or placebo orally 24 and 12 h before vacuum aspiration. In group II (n = 20), cervical biopsies were taken before and after two doses of 100 mg mifepristone or placebo orally 48 and 36 h before vacuum aspiration. Smooth muscle cells, fibroblasts and an extracellular matrix with large bundles of collagen fibrils were the main structural components in all cervical biopsies. In group I, an increased number of mast cells and signs of new blood capillary formation and collagenolysis were observed in several of the biopsies after mifepristone treatment (67% correctly classified). In group II, the effects were less evident and in most of the cases (70%) no definite differences were noted between the biopsies taken before and after mifepristone treatment. Nevertheless, mifepristone treatment had induced softening in the cervical tissue, as judged by the decrease in resistance to mechanical dilatation.