Background: Recent trials of prenatal multivitamin-mineral supplements have yielded mixed findings for outcomes such as birth size, but the benefits of prenatal multivitamin-mineral supplements for maternal outcomes are unknown.
Objective: The main objective of this study was to examine the effect of prenatal multiple micronutrient supplements (MM) compared to iron only (FE) supplements on changes in maternal weight and body composition during pregnancy and the early postpartum period.
Methods: A randomized double-blind clinical trial was conducted in semi-rural Mexico. Women received either MM or FE supplements, 6 days per week from early pregnancy to delivery. Anthropometric measurements were obtained at recruitment, 26 and 37 weeks pregnancy, and 1 month postpartum. Women in both groups were similar at recruitment except that body-mass index (BMI) was greater in the FE group.
Results: Mean weight gain during pregnancy was significantly greater (-0.6 kg) in the MM group (n = 283) compared to the FE group (n = 287), but not after adjusting for maternal BMI at recruitment. Overweight women in the MM group gained 0.53 kg between recruitment and 1 month postpartum, whereas those in the FE group lost 0.63 kg; there were no differences between experimental groups among non-overweight women (p =.06 for interaction).
Conclusions: Compared to iron supplements, MM supplements did not increase weight gain during pregnancy after adjusting for baseline differences in BMI but may lead to greater postpartum weight retention among overweight women.