Predictors of Maternal Weight Gain and Neonatal Body Composition

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.