Marijuana use during pregnancy linked to autism in babies, study says


person smoking marijuana joint

Approximately one in twenty American women have self-reported using marijuana during pregnancy [1]. As weed becomes legalised and more socially acceptable, an increasing number of women are turning to the drug to treat pain and nausea associated with pregnancy, in an effort to avoid medications that may be harmful to their baby [2].

What many women may not be aware of, however, is that marijuana use during pregnancy can have potentially damaging effects on their unborn child.

Marijuana and Pregnancy

Women are now being encouraged to avoid smoking marijuana during pregnancy and lactation over concerns regarding impaired fetal neurodevelopment as well as exposure to the adverse effects of smoking for both the fetus and the mother [3].

As marijuana use has become increasingly normalized, more and more research has gone into understanding the effects of the drug during pregnancy. So far, the results have been quite clear: pregnant women should avoid using marijuana.

Marijuana and Autism

In the largest study that has been conducted to date on the effects of marijuana and pregnancy, researchers found that using marijuana while pregnant may increase the risk that a child will develop autism [4].

The researchers reviewed data from every birth in Ontario, Canada, from 2007 to 2012. They then narrowed their study down to 2 200 women who said they only used marijuana during pregnancy, and did not mix it with tobacco, alcohol, or opioids. It did not look at the amount or type of marijuana used, nor did it consider when during the pregnancy they used it or how frequently. 

Study author, Dr. Darine El-Chaâr, a maternal fetal medicine specialist and clinical investigator at Ottawa Hospital Research Institute in Canada, said that women who used cannabis during pregnancy were 1.5 times more likely to have a child with autism than those who did not.

“These are not reassuring findings. We highly discourage use of cannabis during pregnancy and breastfeeding,” she said [5].

Previous studies have linked marijuna use during pregnancy to other physical and neurological issues like low birth weight, impulsivity, hyperactivity, attention issues, and cognitive and behavioural issues in children [6].

For this reason, El-Chaâr is not surprised by this latest study’s findings, noting that fetal brain development occurs at every stage of gestation.

Marijuana and Stillbirths

Another, older study from 2013 found that using marijuana during pregnancy (as well as other substances like tobacco, prescription painkillers, and illegal drugs) increases the risk of a stillbirth by more than two times [7].

About one in every 160 births in the United States are still births every year, which equates to about 24 thousand stillborn babies annually [8]. While this number has gone down over the last sixty years, the number of stillbirths in the US is still higher than many other developed nations [7].

The researchers in the study did note, however, that they could not entirely separate the effects of tobacco from those of smoking marijuana, however the association was still too strong to be ignored.

“With the legalization of marijuana in some states, it is especially important for pregnant women and health care providers to be aware that cannabis use can increase stillbirth risk,” said senior author Uma M. Reddy, M.D., MPH, of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the NIH institute that supported the study [7].

What We Don’t Know Could Harm Your Baby

According to El-Chaâr, the most common reason expecting mothers use marijuana is for pain management.

“It helps with different conditions that they may have or for nausea and vomiting in pregnancy,” said the doctor. “Some people (said) they use (it) for sleep or for stress reduction. Still others use it recreationally; it’s just part of their routine.” [5]

An analysis of nearly half a million pregnant women in the United States between 2002 and 2017 found that cannabis use among pregnant women more than doubled during that time. They found that the vast majority of use was during the first trimester, but that it was more often recreational than medical [9].

This is problematic, because the first few months of pregnancy might be one of the most sensitive times for an unborn baby’s developing brain. This is because even in a very young fetus, there could be cannabinoid receptors in the brain.

“You can hypothesize that if there are cannabinoid receptors and the baby’s brain is exposed, it may have (an) effect on brain development,” said El-Chaâr [5].

Still more study needs to be done on not only the effects of marijuana use during pregnancy, but also its use while a woman is breastfeeding. The American College of Obstetricians and Gynecologists said in a statement:

“There are insufficient data to evaluate the effects of marijuana use on infants during lactation and breastfeeding, and in the absence of such data, marijuana use is discouraged.” [10]

For the time being, a woman who uses marijuana and becomes pregnant should discuss her use of the drug immediately with her doctor. The ACOG recommends the following:

“Pregnant women or women contemplating pregnancy should be encouraged to discontinue use of marijuana for medicinal purposes in favor of an alternative therapy for which there are better pregnancy-specific safety data,” [10].

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