The incidence of poor fetal growth and adverse maternal and infant birth outcomes is quite high in India, and several lines of evidence suggest that maternal nutritional status may be an important factor. We have previously performed extensive evaluations of poor fetal and infant outcomes in other settings, and found that maternal micronutrient supplementation (B vitamins including vitamin B12, plus vitamins C and E) in HIV positive Tanzanian mothers decreased the risk of low birthweight (<2500 g) by 44% (RR (95% Cl) 0.56 (0.38-0.82)), severe preterm birth (<34 weeks of gestation) by 39% (RR 0.61 (0.38-0.96)), and small size for gestational age at birth by 43% (RR 0.57 (0.39-0.82)). In a prospective cohort study of 410 pregnant Indian women, we recently found a strong relationship between maternal serum vitamin B12 concentration and risk of infant intrauterine growth retardation (IUGR). Compared to women in the highest tertile of serum B12 concentration, women in the lowest tertile were significantly more likely to have IUGR infants, after controlling for maternal age, weight, education, and parity (OR (95% Cl) 5.98 (1.72-20.74)). We now propose a randomized, double-blind trial among 300 pregnant Indian women in order to determine the effectiveness of vitamin B12 supplementation (50 ug daily) in improving maternal B12 status. Secondary aims for this exploratory trial include maternal hemoglobin, maternal weight gain during pregnancy and infant birthweight. All women will receive standard of prenatal obstetric care, including routine supplementation with iron and folate. The study will be a collaborative effort between the Division of Nutrition, St John's Research Institute, Bangalore, India, and the Department of Nutrition, Harvard School of Public Health, Boston, US. Findings from this planned study will be used to design and carry out a larger, more definitive clinical trial, as we have successfully performed elsewhere. As experts in the fields of nutrition, pediatrics, epidemiology and maternal and child health, our team is committed to further evaluating the possible role of micronutrients in improving maternal and child health outcomes in India.