BACKGROUND: Adverse pregnancy outcomes (APOs), including gestational diabetes mellitus (GDM), hypertensive disorders of pregnancy (HDP), small for gestational age (SGA) offspring, preterm birth and placental abruption, pose significant short and long-term health consequences for mothers and their offspring. Engaging in physical activity may reduce the risk of APOs. We aimed to examine the association between objectively measured physical activity before pregnancy and risk of APOs. METHODS: The study population consisted of women with one or more singleton births registered in the Medical Birth Registry of Norway (MBRN) after participating in the fourth survey of the Trøndelag Health Study (HUNT4, 2017-2019). HUNT4 provided data on accelerometer measures on physical activity. We used multivariable adjusted logistic regression models to estimate associations between physical activity (total daily physical activity and metabolic equivalent of task (MET) min/week of moderate to vigorous physical activity (MVPA)) and risk of APOs (GDM, HDP, SGA offspring, preterm birth and/or placental abruption). RESULTS: Among 700 women included in the study population, 145 (20.7%) experienced at least one APO. Compared to women in the lowest tertile of total physical activity/day, those in the highest tertile had lower odds of GDM (OR 0.19; 95% CI: 0.38-0.93) and potentially lower odds of any APO (OR 0.69; 95% CI: 0.43-1.11). Women with higher levels of total daily physical activity and higher levels of MVPA had lower odds for the composite outcome HDP, GDM, and/or SGA (OR 0.49; 95% CI: 0.28-0.87, highest tertile compared to lowest tertile and OR 0.53; 95% CI: 0.28-1.01, > 1000 MET minutes/week compared to < 500 MET minutes/week). CONCLUSIONS: Increased prepregnancy physical activity, including total daily activity, may reduce the risk APOs. Promoting preconceptional everyday activity could be key to improving pregnancy health. Larger studies are needed to confirm these findings.