BACKGROUND: Iron supplementation in pregnancy is a controversial issue. The aim of this review was to summarize the results of relevant papers on this subject. METHODS: Placebo-controlled studies on iron treatment in pregnancy were identified from the Cochrane database. RESULTS: Among fertile women, 20% have iron reserves of >500 mg, which is the required minimum during pregnancy; 40% have iron stores of 100-500 mg, and 40% have virtually no iron stores. The demand for absorbed iron increases from 0.8 mg/day in early pregnancy to 7.5 mg/day in late pregnancy. Dietary iron intake in fertile women is median 9 mg/day, i.e. the majority of women have an intake below the estimated allowance of 12 18 mg/day. Iron absorption increases in pregnancy, but not enough to prevent iron deficiency anemia in 20%, of women not taking supplementary iron. Iron-treated pregnant women have greater iron reserves, higher hemoglobin levels, and a lower prevalence of iron deficiency anemia than placebo-treated women both in pregnancy as well as postpartum. Furthermore, children born to iron-treated mothers have higher serum ferritin levels than those born to placebo-treated mothers. An iron supplement of 65 mg/day from 20 weeks of gestation is adequate to prevent iron deficiency anemia. CONCLUSIONS: In order to avoid iron deficiency in pregnancy, prophylactic iron supplement should be considered. Iron supplements may be administered on a general or selective basis. The selective approach implies screening with serum ferritin in early pregnancy, in order to identify women who can manage without prophylactic iron.