Reproductive
Physical Activity and Risk of Spontaneous Abortion in a Danish Preconception Cohort Marie Dahl Jørgensen* Marie Dahl Jørgensen Ellen M. Mikkelsen Mette Aadahl Søren Brage Jakob Tarp Elizabeth E. Hatch Kenneth J. Rothman Lauren A. Wise Anne Sofie Dam Laursen
Background: About 15-30% of all pregnancies end with spontaneous abortion (SAB), making it one of the most common pregnancy complications. The evidence on the extent to which physical activity (PA) influences risk of SAB is inconsistent.
We evaluated the association between hypothetical replacement of pre-pregnancy sedentary time with different intensities of PA and the risk of SAB using data from a Danish preconception cohort.
Methods: We included 4,724 participants who conceived after entry in the SnartForældre.dk cohort from 2011 to 2023. Participants reported their PA levels via the International Physical Activity Questionnaire at baseline and on bimonthly follow-up questionnaires during preconception. We used data from the most recently completed questionnaire prior to conception. Pregnancy outcomes were identified via follow-up questionnaires, the Danish National Patient Registry, and the Medical Birth Registry.
We used Cox proportional hazards regression models to calculate hazard ratios (HR) and 95% confidence intervals (CI) with gestational weeks as the time scale. We used isotemporal substitution models to examine the effect of replacing durations of sedentary time with walking, moderate PA, and vigorous PA.
Results: The overall risk of SAB was 18% and median gestational age at loss was 7 weeks. The HRs for substitution of 30 minutes of sedentary time/day with 30 minutes of walking, moderate PA, or vigorous PA were 1.01 (95% CI 0.99-1.03), 0.98 (95% CI 0.89-1.09), and 0.91 (95% CI 0.79-1.04), respectively. Among participants with ≥7 hours of sedentary time/weekday, the association for replacement of sedentary time with vigorous PA was stronger (HR 0.80, 95% CI 0.64-1.00).
Conclusion: Replacing 30 minutes of sedentary time/day with walking or moderate PA had little association with risk of SAB. However, replacing sedentary time with vigorous PA was associated with a slightly lower risk of SAB, mainly among participants with ≥7 hours of daily sedentary time.