An iron supplementation trial versus placebo was performed in double blind on 191 attending at 3 month the antenatal clinic of Poissy maternity. Iron status of mothers and newborns was assessed at 3, 5, 7 month, during the delivery and 2 months after the delivery, using biochemical indicators (hemoglobin level, serum ferritin). The compliance was good in 165 pregnant women (86% of the initial sample): 81 in the iron group, 84 in the placebo group. Among the placebo group, anemia (Hb less than 11 g/dl) was observed at the end of the pregnancy in 30% of women. Depletion of iron stores started at 5 month. In the iron group, hemoglobin level increased significantly during the pregnancy and anemia was observed only in 3% of women at the delivery. Iron status of newborns and two months after delivery was related to mothers iron status at delivery and particularly at the 7th month of pregnancy.