The objective: to study pathological changes and compensatory-adaptive reactions in the structural and ultrastructural components of the placental barrier in pregnant women with gestational arterial hypertension, who received magnesium preparations. Materials and methods. 100 patients with gestational hypertension were examined. The presence of magnesium deficiency in these women was determined by the results of our questionnaires.Pathomorphological and electronic microscopic examination of 32 placentas of patients with gestational hypertension was carried out. 12 placentas of them were from pregnant women who received the proposed management of pregnancy, which included magnesium drugs (I group), and 11 placentas – from patients with risk of preeclampsia, who were observed with the use of standard approaches of pregnancy for women with the risk of preeclampsia (II group). Control group included the results of pathomorphological and electronic microscopic study of 9 placentas from healthy women.Results. Placental of women with gestational hypertension have structural features, which is manifested by the mosaic change of placental barrier in the form of uneven circulatory disorders with hemorrhages and stasis (at the ultrastructural level) in the fetal microvessels of the villi, reducing the placental functional area (rapprochement of the villi), presence of stromal sclerosis villi, foci of pathological immaturity, increase in calcium salts (mineral dystrophy) on the background of compensatory reactions. Electronic microscopic study of the placentas in the I group revealed an increase in the compensatory-adaptive reactions of the placenta – thinning of the placental barrier, activation of cytotrophoblast cells in the placental barrier, increase the number of syncytiocapillary membranes in terminal villi with syncytiotrophoblast organic activation, increase in the number of ribosomes, the appearance of orthodox configuration of mitochondria, increasing the number of capillary membranes and thinning of syncytia, reducing the number of sludge phenomena in microvessels, which leads to an increase in the possibility of nutrient transfer from mother to fetus, etc.Conclusions. The use of the proposed therapy, which involves magnesium, diosmin and others substances, leads to a significant decrease in the frequency of detection of pathological changes in structural and ultrastructural components of the placental barrier and increased compensatory-adaptive reactions which can be considered the result of the positive impact of the proposed therapy on the placental ultrastructural elements in women with risk of preeclampsia.