Cannabis use in pregnancy may increase child’s risk for autism

Children whose mothers used cannabis during pregnancy are at a higher risk for autism compared with children whose mothers did not, according to a study published in Nature Medicine.

“Despite these warnings, there is evidence that more people are using cannabis during pregnancy,” Mark Walker, MD, chief of the department of obstetrics, gynecology and newborn care at The Ottawa Hospital and professor at the University of Ottawa, said in a press release. “This is concerning, because we know so little about how cannabis affects pregnant women and their babies. Parents-to-be should inform themselves of the possible risks, and we hope studies like ours can help.”

Walker and colleagues conducted a retrospective analysis of all live births in Ontario, Canada, from April 2007 through March 2012. They used health administrative databases from Ontario containing pregnancy and birth information to determine neurodevelopmental outcomes in children.

A total of 508,025 live births were included in the study, and 497,821 were included in the analyses of autism spectrum disorder and neurodevelopmental disorder after excluding children who lost health insurance access in Ontario or who died before 18 months.

The rate of reported cannabis use during pregnancy was 0.6%.

In the 18-month cohort, 1.4% of children were diagnosed with ASD at the end of the follow-up period, which was a median of 7.4 years among participants.

The researchers found that among children with cannabis exposure in utero, 2.2% were diagnosed with ASD.

They determined that the incidence of ASD diagnosis in children exposed to cannabis in utero was 4 per 1,000 person-years. In comparison, children who were not exposed to cannabis in utero had an ASD incidence of 2.42 per 1,000 person-years.

Walker and colleagues reported that the adjusted hazard ratio for ASD in children who were exposed to cannabis during pregnancy was 1.51 (95% CI, 1.17-1.96) compared with those not exposed to cannabis.

They also conducted an analysis of women who reported using cannabis but no other substances during their pregnancy, and found that children of these women still had a higher risk for ASD compared with those whose mothers did not use cannabis.

According to the researchers, the incidence of intellectual disability and learning disorders were also higher in children exposed to cannabis during pregnancy, but these findings were not as statistically robust.

“In the past, we haven't had good data on the effect of cannabis on pregnancies,” Daniel Corsi, PhD, an epidemiologist at The Ottawa Hospital, said in the press release. “This is one of the largest studies on this topic to date. We hope our findings will help women and their healthcare providers make informed decisions.”