Background: no multicenter studies to assess the prevalence of Magnesium (Mg) deficiency in the general population, particularly among pregnant women have been previously conducted in Russia. Objectives: to evaluate Mg deficiency incidence and management in a pregnant population monitored in Russian polyclinics. Materials and Methods: pregnant women (at any trimester) aged over 18 years were included. Mg deficiencies due to any other concomitant condition were exclusion criteria. Data coming from medical records were collected at Visit 1 and visit 2 (1 month +/- 1 week): complete medical history; diagnosis of Mg deficiency confirmed by serum Mg level (<0.7 mmol/l) routine laboratory tests performed in the course of current practice (blood count, Mg plasma determination and urinalysis) and evaluation of total score (superior 30) using a structured 28 questions self-administrated Magnesium Deficiency Questionnaire (MDQ). Spontaneous reports of adverse reactions were collected. The statistical tests were applied according to type of variable distribution (the Shapiro-Wilkestest) and the estimation of equality of variances (Levene's test of Homogeneity of Variance). If two terms were true the Student’s t-test was used, alternatively the Wilcoxon-Mann-Whitney-Test was used. Paired samples t-test or Wilcoxon test were run for the comparison of changes in study continuous variables. Chi-square (χ2) and Fischer's exact tests were used for comparisons of categorical data. Results: 1130 pregnant women, mean age 28.95±5 years were included. Estimated combining prevalence of Mg deficiency according to the blood plasma levels (<0.7 mmol) and MDQ was 81,2%. It was observed that physicians commonly prescribe different organic Mg salts to pregnant women with Mg deficiency as a routine practice. Thus, Mg was prescribed to 1110 pregnant women: 84.1% received Mg Citrate (933/1110) and 21.3% (177/1110) Mg lactate. At the 1 visit the Mg deficiency according to MDQ score analysis was observed in 80.3% (870/1083) and at the end of the program only 5.75% (62/1083; р<0,001) presented Mg deficiency. An improvement of Mg deficiency signs evaluated using a MDQ was observed. Thus, the mean MDQ score significantly decreased by 22.6±11.9 points (Baseline: 15.8±7.9; Final visit 38.3±13.4 points; р<0,001). During the observational registry period one ADR was reported as an allergic dermatitis in a woman receiving Mg Citrate. Conclusions: the study identified a high prevalence of Mg deficiency in pregnant women population. The prevalence of Mg deficiency was 81.2%. It was observed that organic Mg salts are commonly prescribed by physicians to pregnant women with established Mg deficiency and statistically significant improvement in Mg deficiency signs in pregnant women receiving organic Mg salts was observed. To confirm these findings in other populations leaving across the Russian Federation, it is necessary to conduct an additional study with increased sample size, especially considering the age distribution of the population (women of childbearing age) and the life style.