Using marijuana during pregnancy increases the chances of the baby later being diagnosed with an autism spectrum disorder by as much as 50 percent, according to a new study published in the journal Nature Medicine.
As NBC News reported, the study looked at the data from half a million pregnancies in Canada. The focus is among children who were born between 2007 and 2012, which was before cannabis became legal for recreational use in the country. Specifically, the study's authors looked at 503,065 children, of whom 3,148 had mothers who used cannabis while pregnant.
Among the kids, 7,125 were later diagnosed with autism spectrum disorder. Within that group, 1.4 percent had mothers who did not use marijuana while they were pregnant, while 2.2 percent did. Once the researchers ruled out other factors that could muddle the results, they concluded that the risk of autism was increased by 50 percent when mothers used cannabis during pregnancy.
Daniel Corsi, an adjunct professor at the University of Ottawa, a scientist at the Children's Hospital of Ontario Research Institute, and the study's lead author, said that there are cannabinoid receptors in both the mother and the fetus, and that those cannabinoids can cross placental tissue and enter the fetus' bloodstream. That, in turn, could affect the "wiring" of the fetus' brain, Corsi said.
"Cannabis is not a benign drug and any use during pregnancy should be discouraged," he said.
Ziva Cooper, interim director at the UCLA Cannabis Research Initiative, said that it's too early to draw firm conclusions from the results of the study, which she also noted had its limitations.
"This finding gives some clues that exposure to cannabis in utero is associated with autism, but many questions remain," she said.
Similarly, Daniele Fallin, director of the Wendy King Center for Autism and Developmental Disabilities at the Johns Hopkins Bloomberg School of Public Health, noted that the findings are interesting, but that more research is needed.
"This is an interesting first step, but much more work is needed to implicate maternal cannabis use specifically in autism risk," she added.
Dr. Richard Miller, professor of pharmacology at Northwestern University's Feinberg School of Medicine, said that the takeaway from the new study is that women "should really think very carefully about" using cannabis during pregnancy.
Pregnant women using cannabis has been a growing issue in recent years. Last summer, a team of researchers found that the percentage of women who used marijuana while pregnant rose from 1.9 percent in 2009 to 3.4 percent in 2017.