Research investigating body image in pregnant women has generally examined negative body image outcomes, finding pregnant women have more negative body image in early pregnancy compared to mid-to-late pregnancy. There has been a lack of research investigating how constructs of positive body image and self-objectification differ across pregnancy. Positive body image is associated with positive health behaviours (e.g., physical activity); thus, it is important to understand pregnant women's experiences of positive body image. Further, physical activity has been linked to positive body image through an increase in embodiment and a decrease in self-objectification; whether this holds true for the pregnant population is unknown. The purpose of this study was to determine whether body appreciation, self-objectification, and embodiment differed by trimester, and whether physical activity is associated with body appreciation via an increase in embodiment and decrease in self-objectification. Thirty-one women in the first trimester, 55 in the second trimester, and 75 in the third trimester completed measures of body appreciation, self-objectification, embodiment, and physical activity. Multivariate analysis of covariance showed all measures differed by trimester. Post-hoc tests showed body appreciation and embodiment were higher and self-objectification lower in third trimester compared to first trimester. Embodiment was also higher in the third trimester compared to the second trimester. A serial mediation analysis revealed physical activity was associated with higher body appreciation through an increase in embodiment and a decrease in self-objectification. This suggests physical activity could to improve positive body image and its associated health outcomes in pregnant women.