Dr. Ashley Roman: In most cases, iron is prescribed in pregnancy to treat iron-deficiency anemia. Studies have shown that if the mother is anemic she is at higher risk for low birth weight and preterm birth. The goal in prescribing iron is to bring the hemoglobin level into the normal range.
Some providers prescribe pregnant women iron regardless of hemoglobin level. The rationale behind this strategy is to prevent anemia from developing as the pregnancy progresses. But, a recent study in the British Journal of Obstetrics and Gynaecology found that while routine iron supplementation did marginally improve hemoglobin concentrations during the third trimester in non-anemic women, it also increased the risk of high blood pressure in pregnancy and small-for-gestational age babies.
So, for the woman who is not anemic (hemoglobin greater than 13.2 g/dL), there is minimal benefit and possible harm associated with routine iron supplementation, according to this study.