The BBC reports: Taking daily iron supplements during pregnancy can reduce the chances of having a small baby as well as anaemia, says research from Harvard University.
Studies of two million women found that taking even a tiny amount of iron cut the risk of anaemia by 12% and low birth weight by 3%.
Pregnant women in the UK are not given iron supplements unless their iron levels are found to be low.
Serious iron deficiency tends to affect women in poorer countries.
The British Medical Journal study analysed the results of more than 90 randomised trials and studies involving pregnant women in countries including China and Tanzania.