The review examined the biological role of magnesium in providing numerous physiological processes occurring in the human body, as well as in the physiological course of pregnancy. Magnesium deficiency is defined. It was found that tissues with a high concentration of magnesium are the brain, myocardium, connective tissue, muscles, uterus and especially placenta – in pregnancy. The reasons for the high incidence of magnesium deficiency in the population and in pregnant women in particular were dis-cussed. Modern reference values of magnesium level in different biological environments and expediency of complex evaluation of the body magnesium supply are presented. Risk groups of pregnant women with hypomagnesemia in need of magnesium therapy courses have been determined. Efficiency of preeclampsia prevention in pregnant women who received three monthly courses of oral magnesium during pregnancy was shown. Reasonability of prophylaxis of widespread complications of pregnancy (reccurent pregnancy loss, etc.) with application of vitamin-mineral complexes containing magnesium and components of synergistic action is justified. When diagnosing magnesium deficiency, it is necessary to replenish it by means containing organic magnesium salts in combination with pyridoxine in adequate doses. The problem of bioavailability of various organic magnesium compounds in medicinal preparations is considered. The latest data of domestic and foreign scientific literature, including those from the point of view of evidence-based medicine, showing the effectiveness of oral magnesium preparations for the prevention of obstetric complications, are presented. Safety and preference of magnesium citrate use as the most bioavailable substrate for magnesium therapy in pregnant women is justified, recommendations on use of medicines are given.