Nutritional supplementation and the outcome of pregnancy. I. Birth weight.

Colombian women at risk of malnutrition were enrolled in a health care program and randomly assigned to supplementation and control groups at the beginning of the third trimester of pregnancy. The net dietary intake increments resulting from supplementation amounted to 155 cal and 20 g of protein per day. Supplementation had a significant effect on the mean birth weight of male infants, but not that of female infants; the mechanisms responsible for the sex differences remain to be elucidated. The randomized trial design of the experiment and the documented similarity between the experimental and control groups at the onset permit the conclusion that the observed differences were caused by the food supplementation program. The effect of supplementation on maternal weight gain and the association of the latter with birth weight strongly suggest that improved maternal nutrition mediated the effect on birth weight.