Multiple micronutrient supplementation during pregnancy does not lead to greater infant birth size than does iron-only supplementation: a randomized controlled trial in a semirural community in Mexico1–4

Background: Little is known about the benefits of prenatal multivitamin and mineral supplements in reducing low birth weight. Objective: We conducted a randomized, double-blind clinical trial in semirural Mexico to compare the effects of multiple micronutrient (MM) supplements with those of iron supplements during pregnancy on birth size. Design: Pregnant women (n = 873) were recruited before 13 wk of gestation and received supplements 6 d/wk at home, as well as routine antenatal care, until delivery. Both supplements contained 60 mg Fe, but the MM group also received 1–1.5 times the recommended dietary allowances of several micronutrients. Results: At recruitment, the women in the 2 groups were not significantly different in age, parity, economic status, height, or hemoglobin concentration but differed significantly in marital status (4.6% and 2.0% of women in the MM and iron-only groups, respectively, were single mothers) and mean (± SD) body mass index (in kg/m2; 24.6 ± 4.3 and 23.8 ± 3.9 in the iron-only and MM groups, respectively). Losses to follow-up (25%) and compliance (95%) did not differ significantly between the groups. In intent-to-treat analyses (MM group: n = 323; iron-only group: n = 322), mean (± SD) birth weight (2.981 ± 0.391 and 2.977 ± 0.393 kg in the MM and iron-only groups, respectively) and birth length (48.61 ± 1.82 and 48.66 ± 1.83 cm in the MM and iron-only groups, respectively) did not differ significantly between the groups. Conclusion: These findings suggest that MM supplementation during pregnancy does not lead to greater infant birth size than does iron-only supplementation. Am J Clin Nutr 2003;77:720–5.