Maternal nutrition and fetal growth: the role of iron status and intake during pregnancy

Fetal growth restriction is an important predictor of infant mortality and morbidity. Maternal iron status and iron supplementation during pregnancy have been related to fetal growth with contrasting results. Therefore, indication of iron supplementation, doses, and timing is still controversial. Current literature was reviewed in PubMed/MEDLINE using the following terms: "iron" or "iron deficiency" or "anemia" or "iron intake" or "iron supplementation" and "pregnancy" or "maternal" and "fetal growth"or "birth weight" or "pregnancy outcomes" or "birth outcomes." The search was limited to studies in humans since 1991 assessing iron status or supplementation in the periconceptional period or at any time during pregnancy. Evidence suggests that iron deficiency in early pregnancy has an adverse effect on fetal growth. On the other hand, high levels of maternal iron markers have shown a deleterious effect at different stages of pregnancy. The mechanisms underlying such effect are unclear. It is important to acknowledge the need to assess markers of iron status adequately in order to reach reliable conclusions regarding their relationship with fetal growth. In regard to supplementation, it has been shown that low or moderate doses of iron in early pregnancy have a positive effect on fetal growth, regardless of maternal iron status. No such effect has been seen in trials of supplementation later in pregnancy, with low or high doses. Nevertheless, results should be interpreted with caution as some randomized controlled trials lack adequate methodology. Studies assessing the effect of iron supplementation in early pregnancy on fetal growth in iron-deficient and iron-sufficient women are needed in order to establish the most appropriate indications for doses and timing.