Iron

Incremental iron requirements for the mother and fetus are relatively well established, although how these requirements should be met is more controversial. It is generally accepted that the mother needs to absorb an additional 6 mg/day to supply the amount retained by the fetus (300 mg) and placenta (60 mg) and that used to synthesize additional maternal erythrocytes (450 mg) and replace blood loss during delivery (200 mg). Some iron is saved by the lack of menstruation in pregnancy. The fetus obtains iron from the placenta in a process that involves iron transfer from maternal transferrin to transferrin receptors on the placenta, endocytosis of holotrans-ferrin, and release of iron into the fetal circulation. Maternal iron absorption and transfer to the fetus increases during the second and third trimesters. This process is upregulated if the mother is iron deficient, although in recent years it has become apparent that maternal iron deficiency does reduce the amount of fetal iron stored at birth and available to the fetus during the first months of life.

The EAR for pregnancy is set at 23 mg/day for adolescents and 22 mg/day for adult women, and the RDA is 27mg/day for both groups. Although the requirement is mainly in the last trimester, it is important to build iron stores early and to avoid high doses later, so the higher intake recommendation is distributed throughout pregnancy. The UL is the same as that for the nonpregnant woman and is based on the need to avoid gastrointestinal distress.

It has been calculated that the maternal diet can supply enough iron to meet these increased needs during pregnancy, especially if maternal iron stores are adequate at conception. For this reason, the United Kingdom does not recommend that iron intake be increased during pregnancy, except when there is evidence of iron deficiency anemia. Iron deficiency anemia is a relatively common occurrence during pregnancy, especially in the following situations: Maternal iron status is poor at conception, and maternal diet is low in absorbable iron including heme iron from meat, fish, and poultry. The World Health Organization estimates that approximately 18% of women in industrialized countries and 35-75% of those in developing countries develop iron deficiency anemia during pregnancy. In the United States, the Centers for Disease Control and Prevention reports that anemia affects 10% of low-income women in the first trimester, 14% in the second, and 33% in the last, with a much higher proportion of women becoming iron depleted by term. Accepted cut points for adequate hemoglobin concentration are 110 g/l in trimesters 1 and 3 and 105 g/l in trimester 2 due to midpregnancy hemodilution.

In most countries, iron supplements are recommended routinely for all pregnant women. Benefits clearly include reduction of anemia risk, improved maternal and iron status that can persist through the early postpartum period, and possibly some protection against low birth weight. The amount recommended has been reduced from former levels of 60-120 mg to 30 mg for nonanemic women and 60 mg for anemic women. The World Health Organization recommends 60mg/day plus 400 mg folic acid, starting as soon as pregnancy is confirmed, but recognizes that 30 mg/day may be as effective as 60 mg/day. The folic acid recommendation was originally set based on older studies showing development of folate deficiency anemia in women. Although the risk of this anemia is probably low on a global scale, folic acid supplementation is recognized to have other potential benefits. Some countries still recommend iron supplementation only when pregnant women become anemic. There has also been considerable controversy concerning the best time to start supplementation.

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