Using marijuana in pregnancy may heighten baby’s risk of autism
The risk of autism may be greater in babies born to women who used marijuana during pregnancy, a new study suggests.
In an analysis of data from more than 500,000 Canadian mothers and their children, researchers found a 50 percent increase in the risk of autism spectrum disorder in kids whose mothers had used cannabis while pregnant, according to the report, published Monday in Nature Medicine.
“Cannabis is not a benign drug and any use during pregnancy should be discouraged,” the study’s lead author, Daniel Corsi, an adjunct professor at the University of Ottawa and a scientist at the Children’s Hospital of Ontario Research Institute, said.
Growing number of pregnant women using marijuana
“We know that cannabinoids can cross placental tissue and enter the fetal bloodstream,” Corsi said. “There are cannabinoid receptors present in the developing fetus and exposure to cannabis may impact the wiring of the developing brain.”
While it’s known that substance use in pregnant women can affect a fetus’s neurodevelopment, the question of whether cannabis use is a risk factor for autism has not been thoroughly investigated, Daniele Fallin, director of the Wendy Klag Center for Autism and Developmental Disabilities at the Johns Hopkins Bloomberg School of Public Health, said in an email.
Fallin, who was not involved with the new research, said that the observational study cannot prove that cannabis use by pregnant women causes autism. “This is an interesting first step, but much more work is needed to implicate maternal cannabis use specifically in autism risk,” she added.
To take a closer look at possible neurodevelopmental impacts of cannabis on developing fetuses, Corsi and his colleagues reviewed data from all Ontario births that occurred from 2007 to 2012, which was before the drug was legalized in Canada. Their final analysis included 503,065 children, 3,148 of whom had mothers who used cannabis while pregnant.
The children were followed for an average of seven years, during which 7,125 were diagnosed with autism spectrum disorder. The rate of autism diagnoses among children with in utero cannabis exposure was 2.2 percent, as compared to 1.4 percent in those whose mothers did not use the drug during pregnancy.
When the researchers accounted for factors that might skew their results, they found that the risk of autism was increased by 50 percent when mothers used cannabis during pregnancy.
“This finding gives some clues that exposure to cannabis in utero is associated with autism, but many questions remain,” Ziva Cooper, interim director at the UCLA Cannabis Research Initiative, said in an email. She noted that the women in the study were asked to self-report cannabis use, and only asked about it at one point early in their pregnancy.
Still, “these are important findings given the increase of cannabis use in pregnant women,” Cooper, who was not involved with the new research, said.
Last summer, research from Kaiser Permanente Northern California found that cannabis use is on the rise among pregnant women in the U.S. The percentage of women who used the drug while pregnant rose from 1.9 percent in 2009 to 3.4 percent in 2017.
Health A growing number of pregnant women are using marijuana
Canada legalized recreational marijuana use in 2018, a change that will likely lead to an increase in people using the drug, said Dr. Richard Miller, professor of pharmacology at Northwestern University’s Feinberg School of Medicine and author of “Drugged: The Science and Culture Behind Psychotropic Drugs.” The new study raises an important question: Will it be safe for pregnant women to use?
“The main finding — a very newsworthy one — is that the number who might get autism increased by a significant amount,” Miller said. “The take home message of this paper, which I think is fair enough, is that women should really think very carefully about this.”
CORRECTION (Aug. 18, 2020, 10:36 a.m. ET): An earlier version of this article misstated the name of the institution at the Johns Hopkins Bloomberg School of Public Health. It is the Wendy Klag Center for Autism and Developmental Disabilities, not the Wendy King Center for Autism and Developmental Disabilities.
Linda Carroll is a regular health contributor to NBC News and Reuters Health. She is coauthor of “The Concussion Crisis: Anatomy of a Silent Epidemic” and “Out of the Clouds: The Unlikely Horseman and the Unwanted Colt Who Conquered the Sport of Kings.”
Is it safe to smoke pot during pregnancy? Marijuana use during pregnancy was linked to an increased risk of autism in children, a study in Nature Medicine finds.
Researchers urge caution over study linking marijuana to autism
by Laura Dattaro / 18 August 2020
Republish this article
Discuss this article
Sign up for
Rolling research: Pregnant women are increasingly using marijuana, prompting researchers to examine its effects on babies’ development.
Women who use marijuana while pregnant may be more likely to give birth to an autistic child, according to a study published last week in Nature Medicine 1 .
The findings generated widespread press coverage, but researchers are calling for a cautious interpretation of the results — in part because the association surfaced through an analysis of birth records, not a controlled study.
“This is still a database study and it’s not going to answer all the questions,” says lead investigator Daniel Corsi, senior research associate at the Ottawa Hospital Research Institute in Canada. “We don’t have perfect data.”
The findings are “provocative,” particularly given the large study size, says Stephen Sheinkopf, associate professor of psychiatry and human behavior at Brown University in Providence, Rhode Island, who was not involved in the work.
Women are increasingly using marijuana during pregnancy, especially as more states in the United States and other countries legalize its use 2 . The trend has raised questions about how the substance affects fetal development.
But scientists need to take care in communicating the new results, Sheinkopf says: “These are going to be viewed not only by the public but also by policymakers.”
The researchers tracked diagnoses of neurodevelopmental conditions, including autism, in more than 500,000 children born between 2007 and 2012 in Ontario, Canada. They used a birth registry to identify mothers who used cannabis during pregnancy. At a first trimester check-in, 0.6 percent of the mothers in the registry reported that they had.
Corsi and his colleagues also checked whether any of the children in the registry had been diagnosed with autism after age 18 months, or attention deficit hyperactivity disorder (ADHD), intellectual disability or learning disorders after age 4.
Of the half-million registered children, 7,125 were diagnosed with autism, the team found. And, Corsi says, the prevalence of autism was higher among children born to women who had used marijuana during pregnancy: 2.22 percent, compared with 1.41 percent among women who had not.
But marijuana users differed from nonusers in many other ways that could affect pregnancy outcomes: For example, they were far more likely to have a psychiatric condition, and to use other substances, such as alcohol and prescription drugs, during pregnancy.
To control for these potential confounding factors, the researchers pared down the non-user group — from nearly 500,000 to around 170,000 — to match them to the user group more closely.
The association remained after the matching, Corsi says, with 2.45 percent of cannabis-exposed children receiving an autism diagnosis, compared with 1.46 percent of children who were not exposed. It also stood after controlling for other factors, such as examining women who used cannabis but no other substances.
“It’s compelling that their primary finding of that association with autism was able to be upheld,” says Rose Schrott, a doctoral candidate at Duke University in Durham, North Carolina, who was not involved in the research but has studied the effects of marijuana on autism genes 3 . The findings provide a “strong foundation” for additional, more tightly controlled studies, such as in animal models, she says.
There are other confounding factors that the retrospective data can’t capture, Corsi and others say.
For example, the information on a mother’s psychiatric condition only captures her diagnosis, and does not take into account undiagnosed conditions or those in the father or other family members. Also, the socioeconomic status may be skewed because researchers measured it using census data on the area where the mothers lived, rather than individual household income.
And the data on marijuana use indicates only whether a mother used marijuana at all, not how much or often or whether for recreational or medicinal purposes — to treat nausea, for example. Demonstrating that more marijuana use leads to a stronger association with autism would strengthen the finding, says Keely Cheslack-Postava, research scientist at the New York State Psychiatric Institute in New York City, who was not involved in the research.
“It’s a great use of the data that was there, but I would like to see that kind of evidence in the future to help us really assess if this is a true association,” Cheslack-Postava says. As it stands, the study shows that the relationship between marijuana and autism is “a question that deserves further examination.”
The study may underestimate marijuana use, Sheinkopf says, because mothers may be reluctant to report marijuana use during pregnancy due to stigma or concerns about legal repercussions.
“There’s a long history of efforts to harshly criminalize drug use during pregnancy, and this is damaging to mothers and babies because it shunts women from the healthcare system to the legal system in really damaging ways,” he says. “We as clinical scientists need to advocate for the findings to be used to improve healthcare and not for the purposes of criminalization of moms.”
Future studies could examine cannabis use in a research setting, where privacy may be better protected than it is in a doctor’s office. Corsi is also planning studies that use blood or urine samples to precisely measure cannabis levels during pregnancy.
Women who use marijuana while pregnant may be more likely to give birth to an autistic child. But investigators call for a cautious interpretation of the results.