Iron deficiency during pregnancy affects an important proportion of women in low economic level countries (38 to 88 % according to countries) and still affects as much as 18 % of pregnant women in industralised countries. Inadapted supplies, related to diets poor in food-iron bioavailability, are responsible for iron deficiency before pregnancy. Metabolic adjustments (mobilisation of iron stores, increased absorption), are merely inapt to face the increment of needs. The issue of the influence of this deficiency on the conceptus is still controversial. Numerous arguments, among whom the evaluation of erythrocyte ferritin, favor the hypothesis that the level of newborn’s iron stores is in relation with maternal iron status. Exogenous iron supply is thus necessary, to prevent anemia both in pregnancy and in infancy. In industrialised countries, pregnant women should be prescribed iron supplement during the third trimester, when the needs are prominent. In developing countries, supplementation should be initiated earlier, as soon as possible, because of the high prevalence of iron depleted women at the onset of pregnancy.