Prepregnancy Body Mass Index, Pregnancy Physical Activity Trajectories, and Postpartum Blood Pressure.

BACKGROUND: How prepregnancy body mass index (BMI) and pregnancy physical activity (PA) jointly shape postpartum cardiovascular risk remains unclear. This study evaluated whether joint trajectories of PA and sedentary behavior during pregnancy mediate the association between prepregnancy BMI and postpartum blood pressure (BP). METHODS: Pregnancy 24/7 is a multisite observational cohort enrolling individuals <13 weeks' gestation, aged 18 to 45 years, without chronic hypertension, diabetes, sleep disorders, or severe mobility limitation (n=500). Participants with valid PA/sedentary behavior data for ≥1 trimester and a clinic BP reading 4 to 8 weeks postpartum were analyzed. Prepregnancy BMI was chart-abstracted; PA/sedentary behavior were measured each trimester via the activPAL3 micro. Hypertensive postpartum BP was defined as systolic BP ≥130 mm Hg or diastolic BP ≥80 mm Hg. Parallel-process latent growth modeling and K-means clustering identified PA trajectory groups; mediation analysis tested whether these groups explained the BMI-BP association. RESULTS: Among 388 participants (aged 30.9±4.5 years), 109 (28.4%) had hypertensive postpartum BP. Each 1-unit increase in prepregnancy BMI was associated with 6.0% greater risk of hypertensive postpartum BP (risk ratio, 1.06 [95% CI, 1.04-1.09]), adjusting for demographic and pregnancy characteristics. Three trajectory groups emerged: active-declining (n=142), active-improving (n=103), and consistently sedentary (n=143). The active-declining group had 37% lower risk than the consistently sedentary group, but this attenuated after BMI adjustment. Physical activity trajectories did not mediate the BMI-BP relationship, which was largely explained by prepregnancy BMI alone. CONCLUSIONS: Prepregnancy BMI predicted hypertensive postpartum BP independent of activity patterns, underscoring the clinical value of prepregnancy weight optimization and vigilant postpartum monitoring for those entering pregnancy with elevated BMI. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04749849.