Weight Gain During Pregnancy and Severe Maternal Morbidity

Importance: Severe maternal morbidity (SMM) carries serious consequences for pregnant individuals, yet the association between gestational weight gain (GWG) and SMM remains poorly understood.

Objective

To examine the association between GWG and SMM across prepregnancy body mass index (BMI) categories. Design, setting, and participants: This retrospective cohort study used linked birth registry data from Better Outcomes Registry & Network Ontario and hospitalization data from the Canadian Institute for Health Information for singleton pregnancies with a hospital delivery at a gestational age of 20 weeks or greater in Ontario, Canada, from April 1, 2012, to March 31, 2022. Data were analyzed from May 1 to November 1, 2025. Exposures: Continuous GWG as mean weekly gain in the second and third trimesters and categorical GWG (inadequate, adequate, or excessive) according to the 2009 Institute of Medicine recommendations based on prepregnancy BMI. Main outcomes and measures: SMM, defined as a composite of 13 indicators per the Canadian Perinatal Surveillance System, occurring during delivery hospitalization.