Moderate to vigorous intensity physical activity is known to reduce the risk of hypertensive disorders of pregnancy and other adverse pregnancy outcomes that increase future maternal cardiovascular disease risk (2018 Physical Activity Guidelines Advisory Committee, 2018; Davenport et al., 2018), yet less than 25% of pregnant women meet public health physical activity guidelines (Hesketh \& Evenson, 2016). More than 95% of the 24-hour day is spent in sedentary behavior, sleep, or light-intensity activity; however, the impacts of these lower intensity activities on adverse pregnancy outcomes are unknown. This multi-site observational cohort study (N=500) will leverage state-of-the-art, 24-hour behavior assessment in each trimester of pregnancy and examine associations with adverse pregnancy outcomes to inform guidelines and future interventions designed to improve women's pregnancy and long-term cardiovascular health.