Pre‐pregnancy participation and performance in world's largest cross‐country ski race as a proxy for physical exercise and fitness, and perinatal outcomes: Prospective registry‐based cohort study

Abstract

Objective Investigate associations between pre‐pregnancy participation and performance in a demanding cross‐country ski race (proxy for exercise volume and fitness) and perinatal outcomes. Pre‐registered protocol: osf.io/aywg2. Design Prospective cohort study. Setting Based on entire overlap between the Vasaloppet registry and the population‐based Swedish Pregnancy Register. Sample All female Vasaloppet participants 1991–2017 with subsequent singleton delivery (skiers), and age‐ and county‐matched non‐skiers. Methods We calculated odds ratios (ORs) for non‐skiers versus skiers (model 1) and, among skiers, by performance (model 2), in Bayesian logistic regressions adjusted for socio‐demographics, lifestyle factors, and comorbidities. We repeated calculations adjusting for early pregnancy body mass index (potential mediator) and explored robustness (selection/exposure settings; multiple comparisons correction). Main outcome measures Twenty‐nine important perinatal outcomes, predefined based on existing expert consensus. Results Non‐skiers (n = 194 384) versus skiers (n = 15 377) (and slower versus faster performance, not shown) consistently had higher odds of gestational diabetes mellitus (GDM) (OR 1.70, 95% highest density interval: 1.40–2.09), excessive gestational weight gain (GWG) (1.28, 1.22–1.38), psychiatric morbidity (1.60, 1.49–1.72), any caesarean section (CS) (1.34, 1.28–1.40), elective CS (1.39, 1.29–1.49), and large‐for‐gestational‐age babies (>90th percentile, 1.11, 1.04–1.18); lower odds of inadequate GWG (0.83, 0.79–0.88); and no associations with fetal/neonatal complications (e.g. preterm birth [1.09, 0.98–1.20], small for gestational age [SGA] [1.23, 1.05–1.45]). Adjustment for body mass index attenuated associations with excessive (1.20, 1.14–1.30) and inadequate GWG (0.87, 0.83–0.92) and large for gestational age (1.07, 1.00–1.13). Conclusion Non‐skiers compared with skiers, and slower versus faster performance, consistently displayed higher odds of GDM, excessive GWG, psychiatric morbidity, CS and large‐for‐gestational‐age babies; and lower odds of inadequate GWG, after adjustment for socio‐demographic and lifestyle factors and comorbidities. There were no associations with fetal/neonatal complications.