Anemia of pregnancy is defined as a hemoglobin concentration of less than 11 g/dL in the first and third trimesters, and less than 10.5 g/dL in the second trimester. The rates of anemia are variable and depend largely on preexisting iron stores and supplementation. Estimates from the World Health Organization report that 35% to 75% of pregnant women in developing countries and 18% of women from industrialized countries are anemic. Maternal anemia is associated with an increased risk of preterm birth, low birthweight, and small for gestational age infants. Many studies have shown improvement in these outcomes with maternal iron supplementation in cases of iron-deficiency anemia. Mounting evidence also indicates that maternal iron deficiency in pregnancy reduces fetal iron stores, perhaps well into the first year of life.