Taking daily iron supplements during pregnancy can reduce the chances of having a small baby as well as anemia, says research from Harvard University.
Studies of two million women found that taking even a tiny amount of iron cut the risk of anemia by 12 percent and low birth weight by 3 percent.
Pregnant women in the U.K. 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 analyzed the results of more than 90 random trials and studies involving pregnant women, including mothers-to-be from China and Tanzania.
For every additional 10mg of iron taken each day, up to a maximum of 66mg per day, the risks of anemia and low birth weight decreased, the study found.
Birth weight was found to increase by 15g with each 10mg of iron taken per day.
But researchers found no reduction in the risk of premature birth as a result of iron supplements.
Previous studies have suggested there could be a higher risk of low birth weight and premature birth in pregnant women with anemia.
The study says iron deficiency is the most common cause of anemia during pregnancy, especially in low and middle-income countries, affecting about 32 million pregnant women in 2011.
The study authors are calling for improved antenatal care in countries where iron deficiency is common and they say future research should look at “feasible strategies of iron delivery”.
The World Health Organization currently recommends a dose of 60mg per day for pregnant women.
Dr. Batool Haider, study author from the Department of Epidemiology and Nutrition at Harvard University’s School of Public Health, said even high-income countries could take something from the research.
“The recently estimated prevalence of iron deficiency anemia during pregnancy in Europe was estimated to be 16.2 percent in 2011,” she said.