From the Journals

How has cannabis legalization affected pregnant mothers?



After Canada legalized recreational cannabis in 2018, the rate of acute care for cannabis use during pregnancy in Ontario nearly doubled, data indicate.

A population-based study shows that the rate of cannabis-related acute care use during pregnancy increased from 11 per 100,000 pregnancies before legalization to 20 per 100,000 pregnancies afterward: an increase of 82%. Absolute increases were small, however.

“Our findings are consistent with studies highlighting that cannabis use during pregnancy has been increasing in North America, and this study suggests that cannabis legalization might contribute to and accelerate such trends,” study author Daniel Myran, MD, MPH, a public health and preventive medicine physician at the University of Ottawa in Ontario, said in an interview.

Dr. Daniel Myran, University of Ottawa in Ontario University of Ottawa

Dr. Daniel Myran

The study was published online in the Canadian Medical Association Journal.

Risks for newborns

In a 2019 study, 7% of U.S. women reported using cannabis during pregnancy during 2016-2017, which was double the rate of 3.4% for 2002-2003.

Dr. Myran and colleagues hypothesized that legalizing nonmedical cannabis has affected the drug’s use during pregnancy in Ontario. “We also hypothesized that hospital care for cannabis use would be associated with adverse neonatal outcomes, even after adjusting for other important risk factors that may differ between people with and without cannabis use,” he said.

The researchers’ repeated cross-sectional analysis evaluated changes in the number of pregnant people who received acute care from January 2015 to July 2021 among all patients who were eligible for Ontario’s public health coverage. The final study cohort included 691,242 pregnant patients, of whom 533 had at least one pregnancy with cannabis-related acute care visits. These mothers had a mean age of 24 years vs. 30 for their counterparts with no such visits.

Using segmented regression, the researchers compared changes in the quarterly rate of pregnant people with acute care related to cannabis use (the primary outcome) with those of acute care for mental health conditions or for noncannabis substance use (the control conditions).

“Severe morning sickness was a major risk factor for care in the emergency department or hospital for cannabis use,” said Dr. Myran. “Prior work has found that people who use cannabis during pregnancy often state that it was used to manage challenging symptoms of pregnancy such as morning sickness.”

Most acute care events (72.2%) were emergency department visits. The most common reasons for acute care were harmful cannabis use (57.6%), followed by cannabis dependence or withdrawal (21.5%), and acute cannabis intoxication (12.8%).

Compared with pregnancies without acute care, those with acute care related to cannabis had higher rates of adverse neonatal outcomes such as birth before 37 weeks’ gestational age (16.9% vs. 7.2%), birth weight at or below the bottom fifth percentile after adjustment for gestational age (12.1% vs. 4.4%), and neonatal intensive care unit admission in the first 28 days of life (31.5% vs. 13%).

An adjusted analysis found that patients younger than 35 years and those living in rural settings or the lowest-income neighborhoods had higher odds of acute cannabis-related care during pregnancy. Patients who received acute care for any substance use or schizophrenia before pregnancy or who accessed outpatient mental health services before pregnancy had higher risk for cannabis-related acute care during pregnancy. Mothers receiving acute care for cannabis also had higher risk for acute care for hyperemesis gravidarum during pregnancy (30.9%).

The rate of acute care for other types of substance use such as alcohol and opioids did not change after cannabis legalization, and acute care for mental health conditions such as anxiety and depression during pregnancy declined by 14%, Dr. Myran noted.

“Physicians who care for pregnant people should consider increasing screening for cannabis use during pregnancy,” said Dr. Myran. “In addition, repeated nonstigmatizing screening and counseling may be indicated for higher-risk groups identified in the study, including pregnancies with severe morning sickness.”


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