Obesity is a significant health issue in the United States with 30% of the US population considered obese defined as a body mass index above 30 kg/m2. Obesity is associated with long term health complications including diabetes and cardiovascular disorders. During pregnancy, obesity is associated with an increased risk of fetal macrosomia and birth injury, as well as increased risk of gestational diabetes, preeclampsia, cesarean birth, and preterm birth. The intrauterine environment has been purported to influence the early childhood and lifelong risk of obesity and the metabolic syndrome (obesity, hyperlipidemia, and insulin resistance [IR]). The Institute of Medicine guidelines for maternal weight gain in pregnancy provide an estimate for population goals, but may be inadequate for individual patient needs. Other factors, such as the degree of maternal IR and resting metabolic rate (RMR) may be more predictive of actual nutritional needs during pregnancy. A better determination of caloric and exercise needs may allow the development of more specific dietary recommendations during pregnancy. Optimal nutrition will result in improved maternal and neonatal outcomes. As the intrauterine environment may have important impacts on neonatal and childhood metabolic and cardiovascular outcomes, creation of a favorable intrauterine environment through optimal maternal nutritional and exercise guidelines may reduce well documented problems such as fetal macrosomia, birth injury, cesarean delivery, and later predisposition toward childhood obesity.

The goal of this pilot trial therefore is to correlate maternal resting metabolic rate, dietary characteristics, and insulin resistance levels with fetal birth weight and body composition in an effort to determine which factors are associated with excessive fat mass in the neonate, placing them at increased lifetime risk of obesity.

We hypothesize that women with lower resting metabolic rates (RMR) in the first trimester will demonstrate a greater maternal weight gain, when adjusted for caloric intake and activity. It is also hypothesized that for a given RMR, the degree of maternal insulin resistance (IR) predicts birthweight adjusted for a given caloric intake. A third hypothesis is that women with increased insulin resistance (measured by HOMA) will result in neonates with larger birth weights and a greater degree of neonatal fat mass as measure by DEXA scan, adjusted for RMR and diet characteristics.