Maternal body fat and water during pregnancy: Do they raise infant birth weight?

OBJECTIVE: Our purpose was to determine the relation to infant birth weight of maternal fat and lean tissue during early and late pregnancy. DESIGN: Total and net maternal pregnancy weight, fat, and water were determ ined from measurements of total body water, body density, and bone mineral mass in 200 women, with the use of a multicompartment model for body fat es timation in early and late pregnancy. Regression modeling was used to deter mine the relation of maternal body composition to birth weight, with contro l for maternal age, height, parity, and race and for infant gestational age and sex. RESULTS: Maternal weight and body water at term were significantly associat ed with infant birth weight, but maternal body fat at term was not. These r elations remained when maternal net values were used for weight, fat, and w ater to eliminate the contribution of the conceptus to these components. CONCLUSION: In well-nourished women delivering at term, maternal body fat n ear term does not contribute significantly to infant birth weight, but mate rnal body water does.