The study, published in the BMJ, looked at data from more than 90 studies, including almost two million people, to find the direct dose-response relationship between iron intake, maternal anaemia and low birth weight babies.
Led by Batool Haider from Harvard School of Public Health, the research team noted that iron deficiency is the most widespread nutritional deficiency in the world, and is the most common cause of anaemia during pregnancy - affecting an estimated 32 million pregnant women globally in 2011.
"Prenatal anaemia and iron deficiency have been identified as one of the preventable risk factors for disease with a substantial disease burden," the team said.
"Our findings suggest that use of iron in women during pregnancy may be used as a preventive strategy to improve maternal haematological status and birth weight."
Haider and his colleagues analysed data from 48 randomised trials (made up of 17,793 women) and 44 cohort studies (with 1,851,682 participants) investigating the effects of prenatal iron supplementation on the risk of anaemia and birth weight.
“This comprehensive meta-analysis … suggests that prenatal iron use is associated with a significant increase in birth weight and reduction in risk of low birth weight,” said Haider and his team, noting that a dose-response relationship “of higher iron dose with increasing birth weight and decreasing risk of low birth weight exists.”
“An exposure-response relation also exists between increasing mean haemoglobin concentration in the prenatal period and higher birth weight,” they confirmed.
The team also found evidence of significant reductions in maternal anaemia, iron deficiency, iron deficiency anaemia, in a linear dose-response fashion up to levels of 66 mg per day. There was, however, no reduction in risk of preterm birth as a result of iron use.
Further analysis indicated that for every 10 mg increase in iron dose per day - up to 66 mg – the risk of maternal anaemia was 12% lower, birth weight increased by 15 grams and risk of low birth weight decreased by 3%.
Haider and his team suggested that future research should explore "feasible strategies of iron delivery" as well as "evaluation of the effectiveness of other strategies, such as fortification and dietary diversification."
Published online ahead of print, doi: 10.1136/bmj.f3443
“Anaemia, prenatal iron use, and risk of adverse pregnancy outcomes: systematic review and meta-analysis”
Authors: Batool A Haider, Ibironke Olofin, Molin Wang, et al