Numerous studies suggest that in utero exposures to environmental contaminants are associated with fetal development, congenital anomalies, learning difficulties or other health impacts later in life. Although location and time-activity data have been used to model exposure to specific contaminants in epidemiological studies, little information is available about time-activity patterns of pregnant women. We measured changes in location-based activity patterns over the course of pregnancy (48-h periods, during two or three trimesters) using a self-reported time-activity log among a nonrandom sample of pregnant women (n=62). We assessed the influence of demographics and personal factors on changes in activity over pregnancy using mixed effects regression models. Increasing weeks of pregnancy was a significant predictor for increased time spent at home (1 h/day increase for each trimester of pregnancy), after adjusting for income (2.6 more h/day at home in lowest income group), work status (3.5 more h/day at home for nonworkers) and other children in the family (1.5 more h/day at home with other children). No other measured activities (time outdoors, time in transit modalities or time in other indoor locations) were related to weeks of pregnancy. As our results indicate that pregnant women tend to spend more time at home during the latter stages of pregnancy, future exposure and epidemiological research should consider the potential increase in home-based exposures (i.e., indoor air pollution or chemicals in the home) late in pregnancy, and increased confidence in exposure proxies based on home locations or characteristics during the same period.