Maternal nutrition supplementation during pregnancy interferes with physical resemblance of siblings at birth according to infant sex.

A randomized controlled double-blind study of nutrition supplementation of pregnant and lactating women was conducted in Suilin township, Taiwan. Pregnant mothers were randomly assigned to one of two treatment groups consisting of either a high (800 kcal and 40 g protein) calorie daily supplement or a placebo. For each mother treatment began following the delivery of her first study infant, continued throughout the lactation period; and through the pregnancy and lactation of her second study infant. Comparisons of sibling-sibling anthropometric correlations at birth between groups show that among the placebo group the sibling correlations are statistically significant and of the same magnitude seen in previous studies (approximately 0.5), while among high calorie siblings correlations are unusually low and often not significant. This is particularly true for male fetuses, suggesting that the latter are more sensitive to nutritional environmental variations in utero, than are female fetuses. Reduction in familial correlations, presumed measures of genetic influence, in nutritionally stressed populations, will occur when the environment of relatives differ, but are not due to malnutrition per se.