 This study evaluates the effectiveness of maternal supplementation with Docosahexaenoic acid DHA early in pregnancy to reduce the incidence of deep placentation disorders: preterm birth, preterm labor, preterm premature rupture of membranes, preeclampsia and fetal growth restriction. Half of the participants in early pregnancy will receive DHA 600 mg per day, while the other half will receive placebo. Investigators will study also the ability of DHA supplementation, early in pregnancy, to enhance invasion and transformation of spiral arteries by trophoblast, as deep placentation indicators. 