The authors of a review published by the Cochrane Collaboration analyzed 18 trials comparing the use of intermittent (once, twice, or three times a week on nonconsecutive days) iron supplementation with daily supplementation during pregnancy. In the 18 studies, which involved a total of 4,072 women, subjects received iron and folic acid (12 studies), iron alone (three studies), or iron plus other vitamins and minerals (three studies). A high attrition rate was seen in most of the studies.

Intermittent iron supplementation produced similar results in mothers and babies, regardless of the frequency of supplementation. Regarding the health of the baby, there were no significant differences between the daily and intermittent groups in a number of areas, including birth weight and premature birth. Similarly, there were no differences between the groups in terms of maternal anemia at term. However, women who received intermittent iron supplementation had fewer adverse effects and had a lower risk of high hemoglobin concentrations in the second and third trimesters.

The authors note that the evidence is limited and that the existing trials were of low or very-low quality; they write that "intermittent may be a feasible alternative to daily iron supplementation among those pregnant women who are not [anemic] and have adequate antenatal care."

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