Relation between maternal body composition and birth weight

In order to establish the relationship between maternal body composition indicators (fat-free mass, fat mass, total body water) and birth weight, a cross-sectional study was designed, based on 196 pairs of mothers and live singleton newborns with gestational age of 37 weeks or more. Immediately after delivery, the mothers were interviewed to obtain information about different birth weight predictors. An analysis of maternal body composition through bioelectric impedance was held. Multiple linear regression was used to measure the effect of each variable on birth weight. The birth weight mean was 3,251 +/- 514 g. Maternal height was 160.44 +/- 6.3 cm, total net weight gain was 5.85 +/- 5.15 kg, fat mass consisted of 15.84 +/- 6.72 kg, and fat-free mass was 50.42 +/- 7.65 kg; total body water was 34.82 +/- 5.61 liters. The model which included total body water and all predictors found to be associated with birth weight in the bivariate analysis (maternal age, gestational age, gender, placenta weight, and placenta weight squared) was found to be the best in explaining the variability of birth weight (R(2) = 45.26%). Fat mass was an important predictor only in the subgroup of women within the low tertile of body mass index. In conclusion, fat-free mass and total body water explained a major proportion of the variability of birth weight in comparison with the mother's weight gain during the pregnancy period, which has already been considered an important predictor of birth weight.