Recommended Weight Gain, Maternal Physical Activity and Fetal Growth

Abstract

0284 Both maternal physical activity and weight gain have been shown to Influence birth weight. However, there is little known about how maternal weight gain, with respect to recommended levels, may affect the relationship between maternal physical activity and birth weight. PURPOSE: Our purpose was to examine the Influence of maternal physical activity, in conjunction with recommended weight gain, on fetal growth. METHODS: Women (N = 49) were studied twice during pregnancy (20 and 32 weeks gestation). Physical activity was measured for two consecutive days at each time point by Caltrac accelerometry. Length of time the accelerometers were worn, kilocalories expended during that time, and women's body weights were used to calculate average MET intensities above resting values. Average METs at both time points represented mid-late gestation maternal physical activity. Maternal weight gain from 20 to 32 weeks was determined. Subjects were categorized into prepregnancy weight for height standards (using 12 week post-partum weight as a surrogate for prepregnancy weight) based on 1983 Metropolitan Life Tables (>10% below expected weight for height (n = 7), <10% below and <20% above (n = 29), >20% above (n = 13)). Appropriate rate of weight gain between 20 and 32 weeks gestation was determined using a weight gain grid adjusted for pregravid body size (Georgia Dietetic Association, 1987). Information on birth weight and gestational age at time of delivery was obtained from medical records. Birth weight was adjusted by gestational age, sex, and parity (Zhang & Bowes 1995) in order to calculate fetal growth rate (FGR) for each infant. RESULTS: None of the women, whether gaining more or less than recommended for their body size, delivered low birth weight babies (3720±512.5 g; range 2753g-4943g). FGR increased with increased weight gain, irrespective of pregravid body size (r = 0.46; P<0.001). Physical activity during pregnancy was associated with lower FGR (r = −0.44; P<0.001). Using simple regression analysis we found that maternal physical activity predicted ∼20% of the variance in fetal growth ratio (P<0.001). When weight gain (as a percent of recommended weight gain) was added to the model, an additional 9% of the variance in FGR was explained (r2 = 0.29; P<0.001). CONCLUSION: The amount/intensity of physical activity performed during gestation is inversely related to fetal growth ratio. However, birth weight at any physical activity level was adjusted upward if women gained more weight than recommended during mid-late gestation. Supported by NIH (RO3 HD 35080)