Physical activity and sedentary behavior across 12 months in cohort samples of couples without children, expecting their first child, and expecting their second child.

The onset of parenthood has been reported as a reason for steep declines in moderate-vigorous intensity physical activity (MVPA), but also increases in light activity rather than sedentary behavior. We examined the activity profiles of three cohorts of couples (couples without children, and first-time parents and second time parents) across 12 months. Participants were 314 adults (102 not expecting a child, 136 expecting first-child, 76 expecting second child) who completed baseline demographics and 7-day accelerometry, followed by assessments at 6 and 12 months. Hierarchical linear modeling showed that parents who were expecting their second child had lower MVPA; yet were less sedentary/had higher light intensity activity compared to other couples at baseline. First-time mothers' physical activity pattern changed to match the profiles of parents who were now parenting two children across the first 12 months of child-rearing. Findings support MVPA interventions targeting new mothers.