Effects of Physical Activity on Maternal Lipid Metabolism, Oxidative Stress, and Neonatal Outcomes in Obese Pregnancy

Exercise during pregnancy is associated with the delivery of leaner, lighter, and healthier infants (Clapp 1990, Clapp 2000). Subsequently, high infant adiposity and birth weight are strong predictors of childhood obesity and adult adiposity (Catalano 2006, Danielzk 2002). Therefore, maternal physical inactivity during pregnancy may have significant ramifications for the child, the effects of which may extend well into adulthood. Exercise during pregnancy also plays an important role in the health of the mother. Active pregnant women tend to gain less weight during pregnancy (Clapp 1995) and retain less weight following pregnancy (O'Toole, 2003). With excessive gestational weight gain being the strongest risk factor for maternal overweight and obesity postpartum, as well as being associated with many adverse maternal and neonatal metabolic outcomes such as adiposity and insulin resistance (Heerwagen 2010), the impact of exercise on maternal and neonatal outcomes could be substantial. The mechanisms underlying these changes are poorly understood and studies which strive to expose them are critical.

Habitual physical activity in non-gravid individuals has been shown to positively alter lipid metabolism by increasing fatty acid oxidation (Martin 1996), but the effect of physical activity on maternal lipid metabolism during pregnancy has not been studied. Due to previous research suggesting that an altered intrauterine metabolic environment may play a significant role in fetal programming (Heerwagen 2010), it is reasonable to believe improvements in maternal lipid metabolism may contribute to improved neonatal metabolic outcomes in exercising pregnant women. Preliminary data from our group found that in obese and lean pregnant women, lipid oxidation rate was significantly correlated to offspring birth weight; suggesting maternal lipid metabolism may contribute to neonatal metabolic outcomes. In inactive pregnant women, impaired lipid oxidative capacity in conjunction with known increased physiologic adipose tissue lipolysis that occurs during pregnancy and obesity would result in excess un-oxidized plasma fatty acids that are likely to be re-esterified in adipose tissue and/or delivered to the fetus. This series of events may contribute to increased maternal and neonatal adiposity.

In addition, generation of excess reactive oxygen species, known byproducts of lipid metabolism, may contribute to altered/abnormal oxidative stress profiles in obese pregnant women. Reactive oxygen species are up-regulated during physiologic pregnancy as well as non-gravid obesity, and research suggests oxidative stress may be related to poorer neonatal outcomes (Heerwagen 2010) . In non-gravid individuals, long-term physical activity has been shown to improve oxidative stress profiles (Fisher-Wellman 2009). Therefore, women who exercise during pregnancy may also have higher antioxidant capacity and lower markers of oxidative stress; both of which may contribute to favorable neonatal outcomes. However, this has not yet been studied.

Obesity is also believed to adversely influence lipid metabolism, oxidative stress, and neonatal outcomes in pregnancy. Therefore, we plan to compare these parameters in obese active and obese inactive pregnant women. This study design will allow us to compare groups in order to determine if unfavorable maternal lipid metabolism and oxidative stress profiles, and neonatal metabolic outcomes (adiposity and insulin resistance) are more attributable to physical inactivity or obesity. Previous research with non-gravid adults suggests that the presence of comorbidity is more correlated with physical activity levels than with body weight (Blair 1989, 1999, Sui 2007). This finding is contrary to much of the previous literature on pregnancy which suggests "obesity may be the most common health risk for the developing fetus" (Heerwagen 2010). Knowledge about maternal lipid metabolism and oxidative stress profiles and their relationships in neonatal outcomes in active and inactive pregnant women can guide lifestyle and medical interventions designed to target factors that may be contributing to poor outcomes in obese pregnancy. Currently, we have collected data on lean, inactive pregnant women that can be used for comparison at the end of all data collection.

This is the first study to examine the relationship between physical activity, lipid metabolism and oxidative stress in obese pregnancy. We anticipate that results from the proposed study will demonstrate the importance of a physically active lifestyle during pregnancy (irrespective of body weight) in order to maximize the short and long-term health of the neonate. In addition, we hope that these results will encourage obese and overweight women of childbearing age to remain or become physically active by demonstrating that physical inactivity has a greater effect on poor neonatal outcomes than obesity. These findings are unique as much of the current literature focuses on the negative impact of maternal obesity on neonatal outcomes. Blair et al. has consistently demonstrated in non-gravid populations that physical inactivity is a stronger predictor of all-cause mortality than obesity (Blair 1989, 1999). Similarly, we believe physical activity in pregnancy is more important than simply maintaining a healthy body weight in improving neonatal outcomes. This idea is novel and innovative as it is previously unexplored in pregnancy and pregnancy outcomes.