Physical activity (PA) naturally declines during pregnancy and its effects on infant size are unclear, especially in overweight or obese pregnancies, a low-active subpopulation that tends deliver heavier infants. The objective of this study was to evaluate changes in prenatal PA and infant birthweight in a group of overweight or obese pregnant women. We employed a prospective analysis using data from a randomized controlled exercise trial (2001 to 2006) in sedentary, overweight or obese pregnant women in Michigan. Women with complete data on peak oxygen consumption, daily PA (via pedometers) and birthweight were included in the analyses. Change in PA was estimated via repeated measures analyses, and then its influence on infant birthweight was assessed via linear regression. Eighty-nine pregnant women were included and considered low-active (6,579.91 ± 2379.17 steps/day). PA declined from months 4 to 8 (-399.73 ± 371.38 steps∙day-1∙month-1). Analyses showed that the decline in PA (β = -0.28 g, 95%CI: -0.70, 0.25 g, p = .35) was not associated with birthweight. The findings of this study demonstrated that the decline in maternal PA during mid- to late-pregnancy, in overweight or obese women, was unrelated to infant birthweight. Future investigations should employ rigorous measurements of PA and infant anthropometry in this subpopulation.
Keywords: Cardiorespiratory fitness; macrosomia; obesity; prenatal exercise.