• Daniel Thomas Myran, Rhiannon Roberts, Michael Pugliese, Daniel Corsi, Mark Walker, Darine El-Chaâr, Peter Tanuseputro, and Andrea Simpson.
• Clinical Epidemiology Program (Myran, Roberts, Walker, El-Chaâr, Tanuseputro), Ottawa Hospital Research Institute; Department of Family Medicine (Myran), University of Ottawa; ICES uOttawa (Myran, Pugliese, Tanuseputro), Ottawa Hospital Research Institute; Bruyère Research Institute (Myran, Tanuseputro); Department of Obstetrics, Gynecology and Newborn Care (Corsi, El-Chaâr), The Ottawa Hospital; Children's Hospital of Eastern Ontario Research Institute (Corsi, Walker); Better Outcomes Registry and Network (BORN) Ontario (Corsi, Walker); School of Epidemiology and Public Health (Walker, El-Chaâr, Tanuseputro), University of Ottawa; Department of Obstetrics and Gynecology, Faculty of Medicine (Corsi, Walker, El-Chaâr), University of Ottawa, Ottawa, Ont.; Department of Obstetrics & Gynaecology (Simpson), St. Michael's Hospital/Unity Health Toronto; Li Ka Shing Knowledge Institute (Simpson), St. Michael's Hospital/Unity Health Toronto; ICES Central Toronto (Simpson); MAP Centre for Urban Solutions (Simpson), St. Michael's Hospital/Unity Health Toronto, Toronto, Ont. dmyran@ohri.ca.
• CMAJ. 2023 May 23; 195 (20): E699E708E699-E708.

BackgroundCannabis use during pregnancy is increasing, but the contribution of cannabis legalization to these trends is unclear. We sought to determine whether health service utilization related to cannabis use during pregnancy increased after the legalization of nonmedical cannabis in October 2018 in Ontario, Canada.MethodsIn this population-based, repeated cross-sectional study, we evaluated changes in the number of pregnant people who received acute care (emergency department visit or admission to hospital) between January 2015 and July 2021 among all people eligible for the province's public health coverage. We used segmented regression to compare changes in the quarterly rate of pregnant people with acute care related to cannabis use (primary outcome) with the quarterly rates of acute care for mental health conditions or for noncannabis substance use (control conditions). We identified risk factors associated with acute care for cannabis use and the risk of adverse neonatal outcomes using multivariable logistic regression models.ResultsThe mean quarterly rate of acute care for cannabis use during pregnancy increased from 11.0 per 100 000 pregnancies before legalization to 20.0 per 100 000 pregnancies after legalization (incidence rate ratio [IRR] 1.82, 95% confidence interval [CI] 1.44-2.31), while acute care for mental health conditions decreased (IRR 0.86, 95% CI 0.78-0.95) and acute care for noncannabis substance use did not change (IRR 1.03, 95% CI 0.91-1.17). Legalization was not associated with an immediate change, but the quarterly change in rates of pregnancies with acute care for cannabis use increased by 1.13 (95% CI 0.46-1.79) per 100 000 pregnancies after legalization. Pregnant people with acute care for cannabis use had greater odds of having received acute care for hyperemesis gravidarum during their pregnancy than those without acute care for cannabis use (30.9% v. 2.5%, adjusted odds ratio [OR] 9.73, 95% CI 8.01-11.82). Pregnancies with acute care for cannabis use had greater odds of newborns being born preterm (16.9% v. 7.2%, adjusted OR 1.93, 95% CI 1.45-2.56) and of requiring care in the neonatal intensive care unit (31.5% v. 13.0%, adjusted OR 1.94 95% CI 1.54-2.44) than those without acute care for cannabis use.InterpretationThe rate of acute care related to cannabis use during pregnancy almost doubled after legalization of nonmedical cannabis, although absolute increases were small. These findings highlight the need to consider interventions to reduce cannabis use during pregnancy in jurisdictions pursuing legalization.© 2023 CMA Impact Inc. or its licensors.

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