Pregnant women who smoke cannabis nearly double the risk of their baby being born autistic, a new study warns.
In the largest study of its kind, researchers found that children whose mothers reported using cannabis during pregnancy were at a higher risk of autism.
The incidence of autism was four per 1000 person-years among children exposed to cannabis during pregnancy, compared to 2.42 among unexposed children.
“There is some evidence that more people are using cannabis during pregnancy,” said Professor Mark Walker, senior study author at the University of Ottawa in Canada.
This is alarming because we know so little about the effects of cannabis on pregnant women and their babies.
“Parents-to-be should educate themselves about the potential risks, and we hope studies like ours can help.”
A Canadian study found that the rate of autism was twice as high among the children of women who used marijuana during pregnancy, compared to the number of children born to mothers who did not use the drug (file)
The researchers reviewed data from every birth in Ontario between 2007 and 2012, before recreational cannabis was legalized in Canada.
Of the half million women in the study, about 3,000 (0.6 percent) reported using cannabis during pregnancy.
Importantly, these women used nothing but hemp.
The team had previously found that cannabis use during pregnancy was linked to an increased risk of preterm birth.
In that study, they found that women who used cannabis during pregnancy often used other substances, including tobacco, alcohol and opioids.
Given these findings, the researchers in the current study looked specifically at the 2,200 women who reported only using cannabis during pregnancy and no other substances.
The findings, published in the medical journal Nature Medicine. showed that babies born in this group still had an increased risk of autism compared to those who did not use cannabis.
The researchers do not know exactly how much cannabis the women used, how often, at what time during their pregnancy, or how it was consumed.
But as cannabis becomes more socially acceptable, doctors are concerned that some expectant parents believe it could be used to treat morning sickness.
Dr. Daniel Corsi, an epidemiologist at Ottawa Hospital, said, “In the past, we didn’t have good data on the effect of cannabis on pregnancies.”
He added: ‘This is one of the largest studies on this topic to date.
“We hope our findings will help women and their caregivers make informed decisions.”
Autism is quite common, but still poorly understood.
In the US, about one in 59 children born will fall somewhere on the autism spectrum.
About one in 66 children in Canada is autistic and about one in 160 children worldwide.
Research suggests there is likely a genetic basis for autism, which is about four times more common in boys than girls.
But scientists think that exposure in the womb probably plays a role, too.
The effects of cannabis are poorly understood in the same way as the origins of autism.
Although doctors caution against it, cannabis use has not been linked to miscarriage in humans (although animal studies have suggested an increased risk), and the evidence for the link between cannabis and low birth weight is mixed.
However, marijuana use during pregnancy has been linked to an up to 2.3 times greater risk of stillbirth.
The Ottawa Hospital study did not examine how marijuana use during pregnancy could lead to autism in a child, but scientists believe the drug’s interaction with the so-called endocannabinoid system in the nervous system could play a role in the development of the nervous system. conduct disorder. .