Cannabis use in pregnancy linked to autism, study shows

WOMEN who smoke cannabis during pregnancy almost double the risk of their child having autism, a study of half a million births has shown.

The research, published in Nature Medicine, revealed the incidence of autism was four cases for 1,000 people observed in one year who were exposed to cannabis in pregnancy, compared with 2.42 among unexposed children. Researchers reviewed data from every birth in Ontario from 2007 to 2012, before recreational cannabis was legalised in Canada. The children were followed up until 2017 and autism diagnoses were recorded from 18 months.

Of the half a million women in the study, around 3,000 (0.6 per cent) said they used cannabis during pregnancy.

The team had previously found that cannabis use in pregnancy was linked to an increased risk of premature birth.

In that study, they found that women who used cannabis during pregnancy often used other substances including tobacco, alcohol and opioids.

In the new study researchers looked at 2,200 women who said they only used cannabis in pregnancy and no other substances. The findings showed that babies born to this group still had an increased risk of autism compared to those who did not use the drug.

“Children with prenatal cannabis exposure had an increase of 50 per cent in the risk of an autism diagnosis over the study period,” the report said, even when controlling for outside factors.

Researchers warned that the self-reporting method of the study resulted in limitations, as they do not know how much cannabis was used, how often, and at what time during pregnancy.

Prof Mark Walker, of the University of Ottawa, said: “There is evidence that more people are using cannabis during pregnancy. Parents-to-be should inform themselves of the possible risks, and we hope studies like ours can help.”