Since the late 1970s, the Centers for Disease Control and Prevention, along with other U.S. federal health agencies, have warned women that drinking alcohol while pregnant can cause serious problems, from miscarriage and stillbirth to developmental issues. Yet, a 2019 CDC survey estimated that 1 in 9 American women still drink during pregnancy and 3.9% binge drink. Now, a study from Ottawa Hospital Research Institute in Canada raises new concerns that cannabis use during pregnancy can potentially increase the risk of a child developing autism.

“With the legalization of recreational cannabis in many jurisdictions, there is concern about potentially adverse childhood outcomes related to prenatal exposure,” wrote the research team led by Darine El-Chaâr, MD, a maternal fetal medicine specialist and clinical investigator at the Ottawa Hospital Research Institute.

Published this week in the journal Nature , the study found that “[T]he incidence of intellectual disability and learning disorders was higher among offspring of mothers who use cannabis in pregnancy, although less statistically robust.”

Possible connection between autism and cannabis use during pregnancy

Using data from a period between 2007 and 2012, which was before Canada legalized recreational use of marijuana, researchers linked birth registry records that contained marijuana use during pregnancy with Ontario’s provincial health administrative databases, to identify children with neurodevelopmental issues. They found “an association between maternal cannabis use in pregnancy and the incidence of autism spectrum disorder in offspring.” The authors emphasize caution in interpreting these findings though, saying more research is needed.

The CDC estimates that 1 in 20 U.S. women uses marijuana while pregnant. And while the CDC agrees that more research is required to understand how marijuana affects a fetus, existing research shows that using marijuana while pregnant can cause health problems and learning issues as the child grows older.

A research report on the website of the National Institute on Drug Abuse found that there is “no human research connecting marijuana use to the chance of miscarriage, although animal studies indicate that the risk for miscarriage increases if marijuana is used early in the pregnancy.”

However, the NIDA research paper reports that pregnant women who use marijuana have a 2.3 times greater risk of stillbirth. The paper also stated that human research has shown babies born to women who used marijuana while pregnant “display altered responses to visual stimuli, increased trembling, and a high-pitched cry, which could indicate problems with neurological development.”

And while some women are turning to marijuana to help with nausea associated with pregnancy, the NIDA paper says there is no research showing that it is safe to use. “Given the potential of marijuana to negatively impact the developing brain,” the research report concludes, “[T]he American College of Obstetricians and Gynecologists recommends that obstetrician-gynecologists counsel women against using marijuana while trying to get pregnant, during pregnancy, and while they are breast feeding.”