Study: Marijuana Use During Pregnancy Linked To Autism In Children

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Days after the American Heart Association released a statement advising against smoking cannabis products, an extensive study, published Monday in the journal Nature, found that women who used marijuana during pregnancy were 1.5 times more likely to have a child with autism.

Key Facts:

  • Researchers from The Ottawa Hospital and affiliated institutions reviewed data from every birth in Ontario, Canada, between 2007 and 2012, which summed up to more than 500,000, in what is believed to be one of the most extensive studies of its kind.
  • In 2,200 cases the mothers said they used marijuana during pregnancy without mixing it with tobacco, alcohol or opioids.
  • The study found “an association between maternal cannabis use in pregnancy and the incidence of autism spectrum disorder in the offspring.
  • “The incidence of autism spectrum disorder diagnosis was 4.00 per 1,000 person-years among children with exposure compared to 2.42 among unexposed children, and the fully adjusted hazard ratio was 1.51,” according to the study. 
  • According to the U.S. Centers for Disease Control and Prevention, past research has linked the use of marijuana during pregnancy to low birth weight in newborns and hyperactivity, attention issues, and other cognitive and behavioral problems in children. 
  • The number of pregnant women who use cannabis is believed to be on the rise: A study found approximately 1 in 20 women in the U.S. reported using marijuana while pregnant in 2017, double the rate in 2002—and that’s before marijuana became legal in many states.

Crucial Quote: 

“These are not reassuring findings. We highly discourage the use of cannabis during pregnancy and breastfeeding,” said study author Dr. Darine El-Chaâr, a maternal-fetal medicine specialist and clinical investigator at Ottawa Hospital Research Institute in Canada.

Key Background: 

The authors of the Canadian study published Thursday acknowledged that it is limited. It did not capture the amount and type of marijuana the women used or when during the pregnancy or how often women used it. The study does not definitively prove that marijuana use during pregnancy causes autism, only that there is an association between the two factors. Nonetheless, other research has led to similarly disconcerting findings. A National Institutes of Health study back in 2013 found that pregnant women who use marijuana have a 2.3 times greater risk of stillbirth. Last year, a study by the same team of Canadian doctors found that pregnant women who use cannabis are at higher risk of delivering their baby early. "I'm not too surprised by these findings,” Dr. El-Chaâr said. “Fetal brain development occurs throughout all gestational ages.”


Last Wednesday, in a statement published in the AHA journal Circulation, the American Heart Association said it “recommends that people not smoke or vape any substance, including cannabis products, because of the potential harm to the heart, lungs and blood vessels.” Clinical pharmacologist Robert Page II, who chaired the medical writing group for the statement, wrote that using marijuana has “the potential to interfere with prescribed medications” and “trigger cardiovascular conditions or events, such as heart attacks and strokes.” Page added that if individuals choose to use cannabis products, “the oral and topical forms, for which doses can be measured, may reduce some of the potential harms.”

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