Objective: To evaluate the effect of multimicronutrient supplementation for undernourished pregnant women on the birth size of their offspring, incidence of low-birth-weight infants (< 2500 g), and early neonatal morbidity. Design: Randomized, double-blind, placebo-controlled trial. Setting: Tertiary care hospital. Participants: Two hundred pregnant women ( of 13 465 approached) with a body mass index ( calculated as weight in kilograms divided by the square of height in meters) of less than 18.5 and/or a hemoglobin level of 7 to 9 g/dL were enrolled at 24 to 32 weeks of gestation. One hundred forty-six neonates (73.0%) were available for analysis of birth size and 170 (85.0%) for analysis of morbidity in the 7 days after delivery. Intervention: The micronutrient supplementation group (n=99) received a multimicronutrient supplement containing 29 vitamins and minerals once a day, from enrollment until delivery ( median duration, 58 days; interquartile range, 37-77 days; compliance, 87%). The comparison group (n=101) received placebo for 52 ( 1566) days, with 85% compliance. All subjects also received supplements of iron ( given in the form of ferrous sulfate, containing 60 mg of elemental iron), 60 mg/d, and folic acid, 500 mu g/d. Main Outcome Measures: Birth weight, length, midarm circumference, incidence of low birth weight, and early neonatal morbidity. Results: Infants in the micronutrient group were heavier by 98 g (95% confidence interval [CI], -16 to 213 g) and measured 0.80 cm (95% CI, 0.03-1.57 cm) longer and 0.20 cm (95% CI, 0.04-0.36 cm) larger in midarm circumference compared with the placebo group. Incidence of low birth weight declined from 43.1% to 16.2% with multimicronutrient supplementation a (a 70% decrease; relative risk, 0.30; 95% CI, 0.13-0.71; P=.006), and that of early neonatal morbidity declined from 28.0% to 14.8% (a 58% decrease; relative risk, 0.42; 95% CI, 0.19-0.94; P=.04). Conclusion: Compared with iron and folic acid supplementation, the administration of multimicronutrients to undernourished pregnant women may reduce the incidence of low birth weight and early neonatal morbidity.