Composition of gestational weight gain impacts maternal fat retention and infant birth weight.

OBJECTIVE The purpose of this study was to evaluate how changes in gestational weight and body composition affect infant birth weight and maternal fat retention after delivery in underweight, normal-weight and overweight women. STUDY DESIGN We assessed the body composition of 63 women (low body mass index, 17 women; normal body mass index, 34 women; and high body mass index, 12 women) on the basis of measurements of total body nitrogen by prompt-gamma activation analysis, total body potassium by whole body counting, and a multicomponent model based on total body water by deuterium dilution, body volume by densitometry, and bone mineral content by dual energy x-ray absorptiometry (DXA) before pregnancy, at 9, 22, and 36 weeks of gestation, and at 2, 6, and 27 weeks after delivery. Infant weight and length were recorded at birth; infant anthropometry and body composition by DXA were assessed at 2 and 27 weeks of age. RESULTS Gestational weight gain was correlated significantly with gains in total body water, total body potassium, protein, fat-free mass, and fat mass (P=.001-.003). Gains in total body water, total body potassium, protein and fat-free mass did not differ among body mass index groups; however, fat mass gain was higher in the high body mass index group (P=.03). Birth weight was correlated positively with gain in total body water, total body potassium, and fat-free mass (P<.01), but not fat mass. Postpartum weight and fat retention were correlated positively with gestational weight gain (P=.001) and fat mass gain (P=.001) but not with total body water, total body potassium, or fat-free mass gain. CONCLUSION Appropriate, but not excessive, gestational weight gain is needed to optimize infant birth weight and minimize maternal postpartum fat retention.