A systematic review published in 2000 studied the association between maternal anemia and birth weight; however, some results were inconclusive. A review of randomized control trials and cohort studies published in 2013 concluded that daily prenatal iron use substantially improves birth weight in a linear dose–response manner. Thus, a systematic review and meta-analysis of observational epidemiological studies was conducted to contemporarily estimate the relationship between prenatal maternal hemoglobin and birth weight. We searched four electronic databases for observational epidemiological studies, which reported birth weight as an outcome measure and ascertained prenatal maternal anemia by hemoglobin measurement. Thirty-three studies met inclusion criteria. Meta-analysis of five studies showed that neonates born to women with anemia were, on average, 303 g lighter in birth weight than those born to women without anemia (95% CI: 19.20–588.26; I˛ = 91%; five studies; p = 0.04). On the basis of 17 studies, anemia was found to be significantly associated with doubling the risk of low birth weight (OR: 2.37; 95% CI: 1.66–3.38; I˛ = 81%; 17 studies; p < 0.00001), and when restricting the analysis to high study score, a higher magnitude of risk was seen (OR: 3.30; 95% CI: 2.24–4.87; I˛ = 48%; 7 studies; p < 0.00001). From a subgroup analysis, it was found (p = 0.02) that anemia in the first and third trimesters was associated with the increased risk of low birth weight. High hemoglobin levels significantly doubled the risk of low birth weight (OR: 1.84; 95% CI: 1.09–3.12; I˛ = 62%; seven studies, p = 0.02). Hemoglobin needs to be routinely investigated during pregnancy, and women with low levels of hemoglobin should be treated and those with significantly high levels should be monitored to minimize harmful impact on neonatal health.
Birth weight, hemoglobin, anemia, meta-analysis