Birth Outcomes

Considerable work has been focused on the relationship between anemia, iron deficiency, and birth outcomes such as prematurity and intrauterine growth retardation. Severe anemia has been associated with an increased risk of stillbirth and infant mortality [25, 26]. Based on several observational studies there is an increased risk of delivering a preterm and/or low-birth-weight infant for women who are anemic compared to those who are not. Interestingly, a U-shaped relationship has been observed between hemoglobin levels and birth weight in that the risk of delivering a low-birth-weight infant is increased at both the lower and upper end of the hemoglobin distribution. It is important to note, however, that the mechanisms may differ. Specifically, the increased risk at the upper end may not be due to excess iron but rather it may represent inadequate plasma volume expansion [17].

As is the case for maternal mortality, there are very few well-designed controlled trials in which the efficacy of iron supplementation during pregnancy on improving birth outcomes, such as birth weight, has been evaluated [19, 27]. Pena-Rosas and Viteri concluded in a recent review that currently, strong evidence of iron supplementation during pregnancy and improved birth and pregnancy outcomes is lacking, and that further studies are necessary [27]. Nevertheless, a few recent trials provide findings that support routine iron supplementation during pregnancy. In a large cluster, randomized controlled trial that was conducted in Nepal, where the prevalence of anemia and low birth weight are high, the efficacy of different combinations of micronutrient supplements during pregnancy was assessed [28]. Specifically, the prevalence of low birth weight was reduced significantly from 43 to 34% among women who received iron-folate supplements along with vitamin A during pregnancy compared with those in the control group who received only vitamin A. Interestingly, the prevalence of low birth weight was slightly higher among those who received zinc along with iron-folate and vitamin A and similar to those who received a multivitamin-mineral supplement. There were no differences in prematurity. Two recent studies were also conducted in the United States, where the rates of low birth weight are much lower. Iron supplementation is standard practice for all women who are diagnosed as either anemic and/or iron deficient. Thus, in these studies the benefits of prenatal iron supplementation for women who were iron sufficient were evaluated. Both Cogswell et al. [29] and Siega-Riz et al. [30] found that iron supplementation of iron-replete women during pregnancy significantly reduced the prevalence of low birth weight and prematurity by almost half. It should be noted, however, that there were no significant differences in the prevalence of intrauterine growth retardation, suggesting that most of the effect was mediated through the effect on gestational age. These findings clearly support the current practice of universal iron supplementation, but the effect on other pregnancy outcomes is not known.

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