Background: Although physical activity during pregnancy may be beneficial, the prenatal period is a vulnerable time for decreasing physical activity levels and increasing sedentary time. Methods: This longitudinal cohort study measured physical activity using the Global Physical Activity Questionnaire (GPAQ) in singleton, pregnant women in the second (14-18 wk gestation; n = 332) and third trimester (29-33 wk; n = 256). Results: There was a significant decrease in total MVPA (MET mins/wk) between the second and third trimester (P = .01). The majority of physical activity time was spent in walking for transport (80%), and less than 2% in recreational activities. In both trimesters, being married was inversely associated with walking for transport (second trimester: ¿ = -0.12 95% CI = -0.31 to -0.02, third trimester: ¿ = -0.17 95% CI = -0.47 to -0.07) and owning a car was positively associated with recreational physical activity (second trimester: ¿ = 0.16 95% CI = 0.02 to 0.32, third trimester: ¿ = 0.17 95% CI = 0.04 to 0.27). The women spent an average of 5 hours per day sitting. Conclusion: The low and declining levels of physical activity during pregnancy in this population are a concern. Interventions that include lifestyle education and provision of accessible recreational physical activity programs for pregnant women are needed.