Abstract: Objective To observe the effect of mifepristone on ultrastructure of fetal kidney in the second trimester pregnancy. Methods Twenty five normal pregnant women whose pregnancy ranged from 16-28 weeks were randomly divided into 2 groups: control group(n=10) and test group（ n=15 ）.The women in control group were given waterbag to induce labor alone. Test group was divided into 2 groups (test group Ⅰ：n=10, gestation of 16-22 weeks; test group Ⅱ：n=5, gestation of 23-28　weeks). Test group took mifepristone 100 mg orally per day for 3 d, then were given waterbag to induce labor. After delivery of fetus, fetal kidney was separated immediately for observation by transmission electron microscopy.Results In test group Ⅰ, Glomerulus′s cell was swelling and cavitation. Mesangial cell nuclei showed irregular shape and mitochondria swelled, stroma was normal. The thick endothelial cytoplasm, imperforation, thin basal membrane and podocyte matrix cavitation, villus-like podocyte, secondary enation,proximal convoluted tubule nuclei cavitation were found in filtration membrane, intracytoplasm was vacuoles and had lysosomes. Some nuclei and kytoplasm had cavitation in distal convoluted tubule. In test group Ⅱ, Glomerulus′s cell cavitation was seen. Hyperplasia look like arch local. Little mesangial cell nuclei showed irregular shape or light pycnosis. Mitochondrion in cytoplasm was mild swelling, crest fragmentated partly. The cytoplasm showed mild swelling, podocytes were normal, primary and secondary enation, local fusion and mild villus were found in filtration membrane ,proximal convoluted tubule and distal convoluted tubule were normal. Conclusion Mifepristone could take ischemia hypoxia changes in the ultrastructure of fetal kidney in the second trimester pregnancy. The earlier the stage of the fetus is, the more obvious the ultrastructural changes are.

Key words: fetus, kidney, ultrastructure