Maternal hemoglobin and birth weight: systematic review and meta-analysis

pregnancy.[1] Published research showed that maternal iron deficiency affects the health of both mother and child, and further it is likely to be responsible for intrauterine growth reduction, preterm births, cognitive impairments, and nutritional deficiencies.[1,3,4] Hemoglobin (Hb) concentration has been widely used in diagnosing anemia[1]; however, there have been modern advances such as pregnancy ferritin value or erythrocyte indices being introduced in the last decade for detailed diagnosis. A systematic review published in 2000 studied the association between maternal anemia and birth weight; however, some results were inconclusive.[3] A recent review of randomized controlled trials (RCTs) and cohort studies published in 2013 concluded that daily prenatal iron use substantially improves birth weight in a linear dose–response manner.[4] This review showed that iron intake increases mean Hb concentration, reduces the risk of maternal anemia, and importantly also increases the birth weight. Similarly, another systematic review of RCT of iron supplementation published in 2012 outlined that women with iron supplementations were less likely to have low-birth-weight (LBW) babies (weighing 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 2 = 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 2 = 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 2 = 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 2 = 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.