Canadian research raises concerns about increase in ER visits by pregnant people using cannabis

Researchers behind a new study suggesting an increase in hospital visits by pregnant people related to cannabis use say they're concerned about the potential risks, including premature births and low birth weights.

The research paper, published Monday in the Canadian Medical Association Journal, tracked data from close to one million pregnancies in Ontario between January 2015 and July 2021. 

Of those, a small fraction — 540 pregnant people — visited an emergency room or were hospitalized for cannabis use, according to health administrative data compiled by the researchers. Most of those cases, 390, were emergency room visits.

But the rate of acute care hospital visits rose after cannabis was legalized for recreational use in October 2018, from 11 out of every 100,000 pregnancies to 20 per 100,000, the study says.

The lead author, family physician and public health researcher Dr. Daniel Myran, said that while these incidents are rare, they are also serious, and the rising rate is particularly worrying.

"The concern that I have is, these are very severe presentations, and does the increase in these severe presentations represent a much larger increase in general cannabis use during pregnancy?" he told CBC News.

The study notes the most common reason for needing emergency care related to cannabis was harmful substance use, according to the codes used by hospital staff. That was followed by cannabis dependence or withdrawal, and acute intoxication.

Myran, a fellow at the Bruyère Research Institute and The Ottawa Hospital, said the babies born to these patients were more likely to have lower birth weights, premature births or require admission to a neonatal intensive care unit.

"Given the unknown risks of cannabis at this time, the safest course of action is to not use cannabis during pregnancy," he said.

But other researchers caution that more evidence is needed before making any broad recommendations.

The study suggests the biggest risk factor for cannabis use during pregnancy was severe morning sickness, and Myran said women might be self-medicating to relieve their nausea.

Marlena Fejzo, a researcher at the University of Southern California, pointed out that severe forms of nausea and vomiting can also lead to low birth weights and premature births, making it unclear whether cannabis use or an underlying health condition is responsible for the negative outcomes in the Ontario study.

Fejzo is also the science advisor of the Hyperemesis Education and Research Foundation, a non-profit that focuses on a condition of extreme nausea and persistent vomiting called hyperemesis gravidarum, experienced in about one per cent of pregnancies.

"We don't have the answers yet as to whether it's safer to take cannabis than to leave your hyperemesis untreated in pregnancy," she said.