Although universal prenatal supplementation with iron is recommended, an extra intake of iron does not noticeably benefit pregnant women, except when they are anemic（贫血的） . This was observed by researchers of the Institute of Tropical Medicine Antwerp and colleagues who followed more than a thousand pregnant women in Burkina Faso. Our body needs iron to produce hemoglobin（血红蛋白） , the substance in our red blood cells responsible for the transport of oxygen through our body. In Western countries anemia – a shortage of oxygen transporters – is rare, but in Africa up to half of all women are anemic. Of the 1268 pregnant women in this study, 43% was anemic.

Half of those women received daily pills with 60 milligrams of iron (plus folic acid); the other half received 30 mg of iron (plus folic acid, zinc, vitamins A and C and other micronutrients). Chance decided who got what. The women took the pills until 3 months after delivery. At the end of the study, all women ended up with about the same levels of iron in their blood, regardless of how much iron they had taken. They all had around 11 grams of hemoglobin per deciliter of blood, say slightly below normal.

During pregnancy, when also the growing child needs oxygen, women need more iron than normally, certainly towards the end of their pregnancy. But the administration of extra iron to the 'normal' women could not prevent their hemoglobin levels from (slightly) dropping. "The benefit of iron supplements in nonanemic women is unclear", the authors conclude in The American Journal of Clinical Nutrition.

In Africa, where many people are malnourished, and where parasites（寄生虫） also take their part, many women suffer from iron-poor blood. That of course has to be supplemented. In anemic women the pills made the iron levels go up, to the same level as in the other pregnant women: a bit below normal.