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Abstract
A retrospective cohort study was conducted to ascertain the relationship between maternal serum zinc levels and birth weight. The cohort for the study consisted of 476 predominantly black women of low socioeconomic status who had two blood samples taken while they received prenatal care at the Jefferson County Health Department clinics from June to November 1984. The maternal serum zinc in the same subject was measured twice, early (average 16 wks) and later (average 32.5 wks) in pregnancy. The mean serum zinc concentrations were 92.9 ($\pm$18.6) ug/dl and 69.3 ($\pm$15.5) ug/dl early and later in pregnancy, respectively. The rate of change/week in serum zinc was 1.5 ($\pm$1.4) ug/dl. Serum zinc both during early (p = 0.0001) and late (P = 0.0001) pregnancy was a significant independent predictor of birth weight. After adjusting for initial serum zinc level, there was a significant inverse association between the magnitude of rate of change in maternal serum zinc level and birth weight (p = 0.007), i.e., the larger the drop in serum zinc during pregnancy the smaller the infant. Prevalence odds ratios for low birth weight were 8.2 (95% confidence limit 2.4, 27.5) and 5.8 (95% confidence limits 1.8, 16.4) for maternal serum zinc in the lowest quartile versus the highest quartile early and later in pregnancy respectively. Women with serum zinc in the second and third quartiles did not show any significant increased risk of low birth weight. The data in this study suggest a threshold for maternal serum zinc below which the prevalence of low birth weight increases significantly. In this study zinc nutriture was studied among a subset of predominantly black women belonging to low socioeconomic status who are more likely to have marginal zinc nutriture at the beginning of their pregnancies. The results suggest that zinc may have a possible role in the occurrence of low birth weight among infants born to women with low serum zinc levels. Evaluation of serum zinc early in pregnancy may be useful in identifying women at a higher risk of giving birth to a low-birth-weight infant, thus providing an opportunity for early intervention to improve zinc status and pregnancy outcome.
