Iron and pregnancy—a delicate balance
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The review focuses on iron balance during pregnancy and postpartum in the Western affluent societies. Iron status and body iron can be monitored using serum ferritin, haemoglobin, serum soluble transferrin receptors (sTfR) and the sTfR/ferritin ratio. Requirements for absorbed iron increase during pregnancy from 0.8 mg/day in the first trimester to 7.5 mg/day in the third trimester. Average requirement during the entire gestation is ~4.4 mg/day. Intestinal iron absorption increases during pregnancy, but women with ample body iron reserves have lower absorption than those with depleted reserves, so increased absorption is, in part, due to progressive iron depletion. Apparently, women do not change dietary habits when they become pregnant. Non-pregnant Scandinavian women have a median dietary iron intake of ~9 mg/day, i.e. more than 90% of the women have an intake below the recommended ~18 mg/day. Non-pregnant women have a low iron status, 42% have serum ferritin levels ≤30 μg/l, i.e. small or depleted iron reserves and 2–4% have iron deficiency anaemia; only 14–20% have ferritin levels >70 μg/l corresponding to body iron of ≥500 mg. The association between high haemoglobin during gestation and a low birth weight of the newborns is caused by inappropriate haemodilution. In placebo-controlled studies on healthy pregnant women, there is no relationship between the women’s haemoglobin and birth weight of the newborns and no increased frequency of preeclampsia in women taking iron supplements.