Maternal fat, but not lean, mass is increased among overweight/obese women with excess gestational weight gain

BACKGROUND: Weight gain in pregnancy is an essential physiologic adaptation that supports growth and development of a fetus and is distributed among lean mass that includes total body water and fat mass gains. Although gestational weight gain provides a source of energy for the mother and fetus, excess gestational weight gain may underlie reported associations between parity and future metabolic disorders and is linked to postpartum weight retention and insulin resistance. Although weight gain often is proposed as a modifiable variable to mitigate adverse maternal and offspring health outcomes, our knowledge of specific maternal body composition changes with weight gain and the potential metabolic consequences is limited. Furthermore, although gestational weight gain alters maternal body composition, the impact of excess weight gain on fat and lean mass is not well-studied. Understanding the accrual of fat and lean body mass may improve our understanding of the role of excessive gestational weight gain and metabolic dysfunction. OBJECTIVE: The purpose of our study was to quantify the relationship between gestational weight gain and maternal fat and lean body mass accrual and to compare fat and lean body mass accrual according to the 2009 Institute of Medicine Guidelines for Gestational Weight Gain in Pregnancy adherence. We hypothesized that exceeding current weight gain guidelines would be associated with greater fat, compared with lean body, mass accrual. STUDY DESIGN: This is a secondary analysis of a randomized controlled trial of 49 overweight/obese women; all 49 are included in this secondary analysis. Maternal weight and body composition were collected in early (13 0/6 to 16 6/7 weeks gestation) and late (34 0/7 to 36 6/7 weeks gestation) pregnancy with the use of air densitometry. Correlations were drawn between gestational weight gain and change in fat and lean body mass. We compared change in fat and lean body mass by adherence to the 2009 Institute of Medicine Guidelines for Gestational Weight Gain in Pregnancy. Nonparametric tests and chi-square analyses were performed; a probability value of <.05 was significant. RESULTS: Early pregnancy body mass index was 30.3 kg/m(2) (interquartile range [IQR], 28.5-35.2 kg/m(2)); women gained 9.0 kg (IQR, 5.3-13.2 kg). Overweight and obese women were equally likely to gain excess weight (48% vs 35%; P =.6). Weight gain correlated strongly with fat mass change (r = 0.87; P <.001); women with excess vs adequate vs inadequate weight gain had greater fat mass change overall (5.2 [IQR, 4.2-8.1] vs 0.2 [IQR, -0.4-2.2] vs -2.7 [IQR, -5.2- -0.7] kg, respectively; P <.001) and in all pairwise comparisons. Weight gain also correlated with lean body mass change (r = 0.52; P =.001), but women with excess vs adequate weight gain had similar lean body mass change (8.4 [IQR, 7.2-10.1] vs 7.8 [IQR, 6.0-8.7] kg; P =.1). CONCLUSION: Excess gestational weight gain is associated primarily with maternal fat, but not with lean body mass accrual. Our results may help explain the reason that excess gestational weight gain or fat mass accrual is associated with long-term obesity, metabolic dysfunction, and cardiovascular disease risk.