Iron Supplements in Pregnancy Improve Birth Weight in Infants

There is good evidence that iron supplementation during pregnancy can increase maternal hemoglobin levels, decrease the risk of maternal anemia during late pregnancy, and increase birth weight, according to a systematic review and meta-analysis.¹
   
Iron deficiency is the most common cause of anemia during pregnancy worldwide. All women require additional iron during pregnancy, but most women in high-income countries consume enough iron in their diet. However, women from low- and middle-income countries may not have access to iron-rich foods, such as green leafy vegetables.
   
This review and meta-analysis evaluated whether there is a link between use of iron supplements during pregnancy and maternal hemoglobin levels and birth outcomes. There were 48 randomized controlled trials (RCTs) involving 17,793 women and 44 cohort studies involving more than 1.8 million women included in this review. Most of the RCTs compared the use of daily iron supplements with no supplements or placebo. The daily dose of iron ranged from 10 mg to 240 mg in most trials.
   
Women who received iron supplements had hemoglobin concentrations that were an average of 4.59 g/L higher than those of women who received no iron supplements or placebo (36 trials). Analysis of 19 trials showed that maternal risk of anemia was reduced by 50% in pregnant women who received iron supplements. A dose-response relationship was also noted. For every 10-mg increase in daily iron intake, up to 66 mg/d, there was a 12% reduction in risk of maternal anemia.
   
When birth outcomes were examined, women who received iron supplements had a 19% reduced risk of having a low birth weight infant (13 trials). The average birth weight of infants born to women in the iron supplement group was 41.2 g greater than that of infants born to women who did not receive iron. For every 10-mg increase in daily iron intake, birth weight increased by 15.1 g, and the risk of having a low birth weight infant decreased by 3%, reported the review authors.
   
The major findings of the observational studies were that anemia during the first or second trimester of pregnancy was associated with a 29% increased risk of low birth weight baby (6 studies) and with a 21% increased risk of premature birth (7 studies). However, analysis of the RCTs showed that iron supplementation had no effect on the risk of premature birth in this analysis.
   
Overall, there is good evidence supporting the use of iron supplementation during pregnancy.

Pertinent Points:
- Prenatal iron use is associated with a significant increase in birth weight and reduction in risk of low birth weight.
- There is a dose-response relation of higher iron dose with increasing birth weight and decreasing risk of low birth weight.
- An exposure-response relation exists between increasing mean hemoglobin concentration in the prenatal period and higher birth weight.

References:

1. Haider BA, Olofin I, Wang M, et al. Anaemia, prenatal iron use, and risk of adverse pregnancy outcomes: systematic review and meta-analysis. BMJ. 2013;346:f3443.