Adverse Pregnancy Outcomes and Sedentary Behavior, Light-Intensity Physical Activity, and Daily Steps

Importance: Although moderate- to vigorous-intensity physical activity is recommended to reduce the risk of adverse pregnancy outcomes, associations between lower-intensity activities and adverse pregnancy outcomes are not established. Objective: To determine associations between adverse pregnancy outcomes and sedentary behavior (SED), light-intensity physical activity (LPA), and daily steps. Design, Setting, and Participants: Cohort study conducted from 2021 to 2025, involving 470 pregnant volunteers at less than 13 weeks' gestation at university-affiliated medical centers in Iowa, Pennsylvania, and West Virginia. Statistical analyses were conducted between October 2025 and April 2026. Exposures: Device-based SED, LPA, and daily steps were assessed each trimester, using a thigh-worn accelerometer. Participants were separated into groups based on their activity patterns across pregnancy for SED (total, short SED with <60-minute bouts, and long SED with ≥60-minute bouts), LPA durations (total, standing, and ambulatory), and daily steps. Main Outcomes and Measures: Adverse pregnancy outcomes, including hypertensive disorders of pregnancy, gestational diabetes, preterm birth, and infants who were small for gestational age, were abstracted from medical records and physician adjudicated. Multivariable logistic regression models estimated absolute risks (ARs) and the relative risk (RR) of adverse pregnancy outcomes associated with each activity pattern. Results: Participants (N = 470) had a mean (SD) age of 30.7 (4.5) years and 38.3% were of high socioeconomic status; 174 (37.0%) had an adverse pregnancy outcome and 86 (18.3%) had hypertensive disorders of pregnancy. Across trimesters, participants spent the majority of time in SED (mean [SD], 10.1 [1.5] h/d), with 4.6 (1.4) h/d of LPA and 6783 (2481) daily steps. Compared with low SED (AR, 19.0%), high (AR, 42.3%; RR, 2.22 [95% CI, 1.12-4.43]) and very high (AR, 41.6%; RR, 2.19 [95% CI, 1.09-4.40]) SED patterns were associated with more than twice the risk of adverse pregnancy outcomes. Compared with low LPA (AR, 40.3%), the very high LPA pattern was associated with half the risk of adverse pregnancy outcomes (AR, 21.1%; RR, 0.52 [95% CI, 0.30-0.93]). Participants with moderate (AR, 36.2%; RR, 0.76 [95% CI, 0.58-0.99]) and high (AR, 32.2%; RR, 0.67 [95% CI, 0.49-0.92]) daily steps had fewer adverse pregnancy outcomes than the low steps pattern (AR, 47.7%). Associations were similar for hypertensive disorders of pregnancy and across long SED and standing LPA patterns, although short SED and ambulatory LPA patterns were not significantly associated with adverse pregnancy outcomes. Conclusions and Relevance: Among pregnant individuals, sitting less with greater light-intensity movement and steps was associated with significantly lower risks of adverse pregnancy outcomes. Optimizing lighter-intensity activity patterns should be rigorously tested as a strategy to improve pregnancy health.