Children of mothers who use cannabis during pregnancy appear to be at higher risk for autism, according to a study of half a million women.
In the largest study of its kind, researchers found that four in 1,000 children whose mothers used cannabis during pregnancy had an incidence of autism, compared to 2.42 among those whose mothers did not use it.
The study, conducted at the University of Ottawa, looked at data between 2007 and 2012, before recreational use of cannabis was legalized in the region.
The study included 500,000 women, of whom approximately 3,000 reported using cannabis during pregnancy.
The paper also reports that “the incidence of intellectual disability and learning disabilities was higher in the offspring of mothers who used cannabis during pregnancy,” although it indicates that this result is less statistically robust.
Canada has legalized the use of cannabis but recommends that you do not use it if you are pregnant or breastfeeding.
“Despite these warnings, there is evidence that more people use cannabis during pregnancy,” said Dr. Mark Walker, head of the Department of Obstetrics, Gynecology and Neonatal Care at The Ottawa Hospital, professor at University of Ottawa and lead author on the study.
“This is concerning because we know so little about how cannabis affects pregnant women and their babies. Prospective parents should educate themselves about the possible risks and we hope studies like ours can help.
In the study, published in Nature Medicine, the researchers looked at the results of 2,200 women who reported using cannabis and no other substance. However, the study did not take into account how much cannabis was consumed, how often it was used, when it was pregnant and how it was consumed.
Therefore, the study can only show the association, not the cause and effect.
“In the past, we haven’t had good data on the effect of cannabis on pregnancies,” said Dr. Daniel Corsi, epidemiologist at The Ottawa Hospital.
“This is one of the largest studies on this topic to date. We hope that our findings will help women and their health care providers make informed decisions. “