U-Shaped Association between Maternal Hemoglobin and Low Birth Weight in Rural Bangladesh

Abstract

Low birth weight (LBW) is associated with a higher risk of neonatal mortality and the development of adult-onset chronic disease. Understanding the ongoing contribution of maternal hemoglobin (Hgb) levels to the incidence of LBW in South Asia is crucial to achieve the World Health Assembly global nutrition target of a 30% reduction in LBW by 2025. We enrolled pregnant women from the rural Tangail District of Bangladesh in a Maternal Newborn Health Registry established under The Global Network for Women's and Children's Health Research. We measured the Hgb of pregnant women at enrollment and birth weights of all infants born after 20 weeks gestation. Using logistic regression to adjust for multiple potential confounders, we estimated the association between maternal Hgb and the risk of LBW. We obtained Hgb measurements and birth weights from 1,665 mother-child dyads between July 2019 and April 2020. Using trimester-specific cutoffs for anemia, 48.3% of the women were anemic and the mean (±SD) Hgb level was 10.6 (±1.24) g/dL. We identified a U-shaped relationship where the highest risk of LBW was seen at very low (< 7.0 g/dL, OR = 2.00, 95% CI = 0.43-7.01, P = 0.31) and high (> 13.0 g/dL, OR = 2.17, 95% CI = 1.01-4.38, P = 0.036) Hgb levels. The mechanisms underlying this U-shaped association may include decreased plasma expansion during pregnancy and/or iron dysregulation resulting in placental disease. Further research is needed to explain the observed U-shaped relationship, to guide iron supplementation in pregnancy and to minimize the risk of LBW outcomes.

Figure 1.

Diagram of maternal newborn health registry enrollment in Bangladesh, 2019–2020. ^aOf the eligible population for this analysis, 90 women refused to allow a hemoglobin level; ^bAccurate birth weight information was not recorded for 226 neonates (107 of these had birth weight estimates recorded, 63 had birth weights taken after 14 days of life, and 56 neonates had no birth weight recorded).

Figure 2.

U-shaped association of hemoglobin with low birth weight (LBW) outcome. Note: Locally weighted scatterplot smoothing (LOESS) plot of LBW outcome depicting the logit of the estimated probabilities of LBW at given hemoglobin levels, binomial variables are plotted at 0 for normal birth weight (NBW) and 1 for LBW. The current figure is truncated for better viewing of the LOESS curve.