 2. Study the ability of DHA supplementation, early in pregnancy, to enhance invasion and transformation of spiral arteries by trophoblast, as deep placentation indicators. Methodology: investigators will conduct a randomized, placebo controlled, double blind, clinical trial of maternal supplementation with DHA Docosahexaenoic acid to prevent deep placentation disorders. Women will be recruited before 16 weeks of pregnancy from 5 ambulatory centers, 2.400 pregnant women will be assigned to 600 mg DHA per day or placebo. A composite outcome will be the primary outcome of the study. The components of the composite outcome will be: preterm birth 340 weeks gestation; early preeclampsia 340 weeks and severe fetal growth restriction lower than the 2 percentile and 340 weeks. Each of the outcomes of the composite outcome and other clinically relevant maternal and fetal outcomes will be evaluated as the secondary outcomes of the study. Clinical samples will be obtained from pregnant women on both groups, including: plasma, trophoblast, placental bed and myometrium, to study changes of deep placentation or defective placentation markers. Trophoblast cell lines will be used to study the effect of DHA on trophoblast function in vitro. 