Objective: To evaluate whether zinc supplementation during pregnancy is associated with an increase in birth weight.
Design: A randomized double-blind placebo-controlled trial.
Setting: Outpatient clinic and delivery service at the University of Alabama at Birmingham.
Patients: Five hundred eighty medically indigent but otherwise healthy African-American pregnant women with plasma zinc levels below the median at enrollment in prenatal care, randomized at 19 weeks' gestational age. Women were subdivided by the population median body mass index of 26 kg/m2 into two groups for additional analyses.
Intervention: Women who were taking a non-zinc-containing prenatal multivitamin/mineral tablet were randomized to receive either a daily dose of 25 mg of zinc or a placebo until delivery.
Main outcome measures: Birth weight, gestational age at birth, and head circumference at birth.
Results: In all women, infants in the zinc supplement group had a significantly greater birth weight (126 g, P = .03) and head circumference (0.4 cm, P = .02) than infants in the placebo group. In women with a body mass index less than 26 kg/m2, zinc supplementation was associated with a 248-g higher infant birth weight (P = .005) and a 0.7-cm larger infant head circumference (P = .007). Plasma zinc concentrations were significantly higher in the zinc supplement group.
Conclusions: Daily zinc supplementation in women with relatively low plasma zinc concentrations in early pregnancy is associated with greater infant birth weights and head circumferences, with the effect occurring predominantly in women with a body mass index less than 26 kg/m2.