Trajectories of objectively-measured physical activity and sedentary time over the course of pregnancy in women self-identified as inactive

• This study is among the first to describe the trajectory of physical activity and sedentary behavior throughout pregnancy
• Decreased physical activity and increased sedentary time observed in 3rd trimester
• Findings may inform when best to intervene on physical activity during pregnancy

There is a need for investigations that document the daily course of pregnancy-related changes in PA and sedentary behavior. The purpose of this study was to describe the trajectory of PA and sedentary behavior and whether they differ among weight status in pregnant women self-identified as inactive. Eighty inactive pregnant women (8–16 weeks) were recruited from a nationwide text-message intervention. PA was measured using a Fitbit. Chi-square analyses and t-tests were used to analyze univariate demographic and PA variables. Mixed model-repeated measures ANOVA was used to analyze trajectory changes in daily PA and sedentary behavior. Light activity (beta [SE] = 2.79 [0.30], p < .001), active time (b [SE] = 1.62 [0.16], p < .001), and steps (b [SE] = 112.21 [10.66], p < .001) increased during the second trimester followed by a precipitous decline during the third trimester. Sedentary behavior followed an opposite pattern (b = − 9.88 [1.07], p < .001). Overweight and obese women took significantly fewer steps/day (b [SE] = − 742.37 [362.57], p < .05 and − 855.94 [381.25], p < .05, respectively) than normal weight women, and obese women had less “active” minutes/day (~> 3.0 metabolic equivalents; b [SE] = − 12.99 [5.89], p < .05) than normal weight women (P′s < 0.05). Women who self-identify as inactive, become more sedentary and less physically active as pregnancy progresses. This study was among the first to describe the trajectory of daily PA and sedentary behavior throughout pregnancy. This study may help inform health care provider and patient communication related to PA, sedentary behavior, and the time in which to communicate about these behaviors.