Hereditary predisposition is a risk factor for human diseases at different age, including embryonic and fetal periods. One of the indicators of hereditary predisposition may be the presence of polymorphic alleles of the folate cycle enzymes genes.Objective: to develop an algorithm for the prevention of gestational complications, diseases of the newborn by determining the alleles of the folate cycle enzymes genes of biological parents’ organisms, the newborn, and the use of personalized preventive measures.Materials and methods. 100 women and 50 men of the reproductive age have been examined. Group I and Group Ia underwentthe proposed preconception preparation. 100 newborns from women of both groups have been examined. The folate cycle enzymes genes alleles were studied in people of 20 families, the women of which had pregnancy with placental dysfunction, premature detachment of the placenta, the fetal growth retardation syndrome, congenital malformations of the fetus.Results and its discussion. Among women, methylenetetrahydrofalatreductase polymorphism on T allele was detected in 63 (63.0 %) cases: homozygous – in 18 (18.0 %), heterozygous – in 45 (45.0 %); among men correspondingly – in 31 (62.0 %), 11 (22.0 %), 21 (42.0 %) cases. Among newborns, methylenetetrahydrofalatereductase polymorphism on T allele was detected in 65 (65.0 %) cases: homozygous – in 20 (20.0 %), heterozygous – in 45 (45.0 %). The women who underwent the proposed preconception preparation had the significantly reduced 5.2 times frequency of miscarriage threat syndrome, subchorionic hematoma – 7 times. Anembryonic gestation, gestational pyelonephritis, congenital malformations of the fetus, anemia of pregnant women, premature labor, placental dysfunction by the gestation trimesters in the main group were not observed, which confirms the effectiveness of the preparation.Conclusion. The presence of polymorphic alleles of the folate cycle enzymes genes is a risk factor for diseases of the cardiovascular, digestive, urinary, reproductive systems, reproductive disorders, confirms a necessity in a personalized algorithm for preconception preparation and personalized prevention of gestational complications, diseases in children.