Iron requirements are greater in pregnancy than in the nonpregnant state. Although iron requirements are reduced in the first trimester because of the absence of menstruation, they rise steadily thereafter; the total requirement of a 55-kg woman is approximately 1000 mg. Translated into daily needs, the requirement is approximately 0.8 mg Fe in the first trimester, between 4 and 5 mg in the second trimester, and >6 mg in the third trimester. Absorptive behavior changes accordingly: a reduction in iron absorption in the first trimester is followed by a progressive rise in absorption throughout the remainder of pregnancy. The amounts that can be absorbed from even an optimal diet, however, are less than the iron requirements in later pregnancy and a woman must enter pregnancy with iron stores of >/=300 mg if she is to meet her requirements fully. This is more than most women possess, especially in developing countries. Results of controlled studies indicate that the deficit can be met by supplementation, but inadequacies in health care delivery systems have limited the effectiveness of larger-scale interventions. Attempts to improve compliance include the use of a supplement of ferrous sulfate in a hydrocolloid matrix (gastric delivery system, or GDS) and the use of intermittent supplementation. Another approach is intermittent, preventive supplementation aimed at improving the iron status of all women of childbearing age. Like all supplementation strategies, however, this approach has the drawback of depending on delivery systems and good compliance. On a long-term basis, iron fortification offers the most cost-effective option for the future.