29/01/2025
Ottawa, Ontario — Wednesday January 29, 2025
Between 2012 and 2022, Ontario saw a 2.5-fold increase in cannabis use among pregnant women. New study findings show that younger women were more likely to use cannabis while pregnant, but after 2019, which coincides with the legalization of cannabis in Canda, there was a pronounced increase across all age groups.
Reports of cannabis use hit an alarming rate of 24.1% among mothers under nineteen years old in 2020-2021, accompanied by a slight 1% decline the following year.
Despite far-reaching public health campaigns warning of the harmful consequences, tobacco, alcohol and cannabis are still consumed in up to 1 in 10 pregnancies. Prenatal substance use can have dire consequences on the unborn baby, including increased risk of miscarriage, stillbirth, preterm birth, and more.
To better understand prenatal substance trends and behaviours in Ontario, Dr. Daniel Corsi, Scientist at the CHEO Research Institute and Epidemiologist at BORN Ontario, and colleagues reviewed self-reported data from 975,242 pregnant women between 2012 and 2022.
Results from this study, recently published in JAMA Network Open, paint a concerning picture for public health.
Using data from the Better Outcomes Registry and Network (BORN), which is part of CHEO, 12.3% of participants reported having consumed at least one substance during pregnancy. Of the three, tobacco was simultaneously the most used substance, with 9.2% of women reporting having smoked tobacco while pregnant and the substance whose overall use decreased drastically (45.7%) over the ten-year period. Prenatal tobacco use was most common among mothers under the age of nineteen.
Alcohol use remained relatively stable (2.4%), showing similar trends as tobacco and cannabis that younger women were more likely to consume alcohol whilst pregnant.
“When looking at these findings, it’s important we interpret them within a larger social context. Trends in cannabis use coincide with its legalization, which may have impacted the way individuals perceived the risk of using it while pregnant,” said the study’s senior author Dr. Corsi, Associate Professor at the University of Ottawa’s Department of Obstetrics and Gynecology and the School of Epidemiology and Public Health. “We also know that the COVID-19 pandemic led to an increase in substance use across many populations, with pregnant individuals being one of them.”
More research is needed to identify the underlying factors that drive prenatal substance use.
These findings shine a light on the need for increased education and awareness on cannabis use during pregnancy. The overall decline in tobacco use and low reports of alcohol use suggest public health campaigns and policies are effective at limiting prenatal substance use, though greater prevention efforts are needed to target young and first-time mothers, who are shown to be the most likely to use substances while pregnant.
JAMA Netw Open. 2025;8(1):e2455310. doi:10.1001/jamanetworkopen.2024.55310