A large Canadian study found an association between maternal cannabis use during pregnancy and autism spectrum disorder in babies.
The study, published Monday in Nature Medicine, involved an analysis of all live births in Ontario from April 2007 to March 2012, before recreational cannabis was legalized in Canada. The study notes that cannabis use during pregnancy has increased.
Of half a million women in the study, 3,000, or 0.6%, reported using cannabis during pregnancy, according to a hospital press release on the study.
Specifically, researchers found that women who used cannabis during pregnancy were 1.5 times more likely to have a child with autism, per Forbes.
“The incidence of intellectual disability and learning disorders was higher among offspring of mothers who use cannabis in pregnancy, although less statistically robust,” the study authors wrote.
In a separate study conducted by the same researchers, they previously found that cannabis use in pregnancy was linked to an increased risk of preterm birth. The women involved in that study often used other substances like tobacco, alcohol, and opioids.
“Considering those findings, in the current study the researchers specifically looked at 2,200 women who reported using only cannabis during pregnancy, and no other substances. They found that babies born to this group still had an increased risk of autism compared to those who did not use cannabis,” per the press release.
The study had limits, however. Researchers don’t know the amount of cannabis used, the point at which women used cannabis during pregnancy, or how the cannabis was consumed.
Researchers emphasized caution when interpreting the results because, despite efforts to control for other factors, other variables may be at play. The study, therefore, shows association — not cause and effect.
Still, the study’s senior author called the results “concerning.”
“This is concerning because we know so little about how cannabis affects pregnant women and their babies,” said Dr. Mark Walker, chief of the Department of Obstetrics, Gynecology and Newborn Care at The Ottawa Hospital, professor at the University of Ottawa and senior author on the study. “Parents-to-be should inform themselves of the possible risks, and we hope studies like ours can help.”