Associations between maternal physical activity and fitness during pregnancy and infant birthweight

Prenatal physical activity (PA) reduces the risk of delivering infants with a birthweight ≥4000 g among normal-weight pregnant women, but evidence on the impact of maternal cardiorespiratory fitness (CRF) on birthweight remains equivocal among overweight or obese (OW/OB) pregnant women. The purpose of this study was to evaluate the relationship between maternal prenatal PA and CRF and birthweight in OW/OB pregnant women. Data from a randomized controlled exercise intervention trial in sedentary, OW/OB pregnant women were used. Women with complete data (n = 89) on birthweight, peak oxygen consumption (at 17 weeks), and daily PA were selected for analyses. Multiple linear regression models were performed to determine the independent and joint associations of maternal PA and CRF with birthweight while adjusting for gestational age, weight gain, and group allocation. On average, participants were 32 years old, OW/OB (BMI 29.97 ± 7.14 kg/m²), unfit (VO_2peak: 19.85 ± 3.35 ml O₂ kg^-1 min^-1), and led low active lifestyles (6579.91 ± 2379.17 steps/day). Analyses showed that maternal PA (steps·day^-1·month^-1) (β = 0.03 g, 95% CI: -0.03, 0.08 g) and CRF (ml O₂·kg^-1·min^-1) (β = -8.8 g, 95%CI: -42.2, 24.5 g) were neither independently nor jointly (β = 0.006 g, 95%CI: -0.005, 0.02 g) associated with birthweight. Maternal PA and CRF during pregnancy were not related to birthweight in OW/OB pregnant women. The limited variability in maternal PA and CRF and low dose of PA may explain the null findings of this study. Given the paucity of studies examining these relationships in OW/OB pregnant women, more research is warranted.