Cannabis Use in Pregnant Individuals Linked to Autism in Children

pregnant belly with cannabis leafIn the largest study of its kind, researchers found that children whose mothers reported using cannabis during pregnancy were at greater risk of autism. The study, published in Nature Medicine in August 2020, included births in Ontario between 2007 and 2012 (before recreational cannabis was legalized).

Data was sourced from the BORN Information System which lead author, Dr. Daniel Corsi calls “an especially powerful perinatal registry for research - with more than 1 million mother-baby dyads, the BIS is one of the largest data sources of its kind globally".

“We can link data from the BIS to ICES, a world-class data warehouse institution in Ontario. Combining these two resources allows for a very rich data set for analysis from conception, pregnancy, and birth and across the life course”.

The researchers used BIS data, combined with health records from ICES to longitudinally follow more than half a million children in Ontario and look for diagnoses of autism spectrum disorder and other neurodevelopmental problems after exposure to cannabis. They found that the prevalence of autism was higher among children born to women who had used cannabis during pregnancy.

Because cannabis is legal in Ontario, more socially acceptable, and even promoted by some as a treatment for morning sickness, pregnant individuals may not be aware of the risks.

"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" says Dr. Mark Walker, Scientific Director of BORN Ontario and one of the study's authors.

The team has plans for further research: “Although the findings were compelling, we plan to continue the research to address some limitations. For example, we plan to collect blood and urine samples to measure cannabis directly. We are also engaging with other perinatal registries in British Columbia and Nova Scotia to conduct similar studies.”

Dr. Corsi's research has already found its way into Up-to-Date - a clinical decision support tool used by over 1,000,000 physicians in 170 countries. Up-to-Date presents a comprehensive synthesis of the evidence available on a topic, followed by recommendations that can be acted on at the point-of-care. This a great example of knowledge translation: health-care providers using the latest research evidence to help counsel their patients about risk. 

Meet Dr. Daniel Corsi...

Dr. CoDr. Daniel Corsirsi has been interested in substance use research for  years, but started focusing his efforts on cannabis research in 2017, after Canada announced plans to legalize the recreational use of cannabis. He wondered how legalization would affect the use of cannabis among pregnant individuals: “We initially wanted to look at changes in the rates of use over time and eventually compare use before and after legalization. We are also interested in socioeconomic, demographic, and lifestyle factors related to cannabis use”.

 Read more of Dr. Corsi's Story...

Dr. Corsi finds research in this area very rewarding: “I find it exciting to work alongside evolving policy changes around cannabis use and produce research to help develop helpful information to guide patient care”.

With the legalization of cannabis, Dr. Corsi says attitudes have shifted: “The perception is that because it's legal, it's safe. There is a fair amount of social media reporting that cannabis use in pregnancy is safe. Its also been marketed to help with symptoms that individuals experience in pregnancy, such as morning sickness.”

During the first trimester, however, the developing fetus is at risk of the most significant negative impact. Dr. Corsi’s research has shown adverse effects on birth outcomes, including small size at birth, premature birth, and other risks: “Our results also indicate that children with exposure to cannabis in pregnancy may be at higher risk of neurodevelopmental complications, including autism and learning disorders”.

Dr. Corsi acknowledges that this work is not easy: "Scientifically, there are challenges with studying the health effects of cannabis use or substance use generally, areas where it would not be ethical to do a clinical trial. So we have to recognize and understand the limitations of epidemiology. We continuously examine and try to improve our research to get the correct answer."