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• Posted December 12, 2023

Using Marijuana While Pregnant Raises Complications Risk

Marijuana use by expecting moms is associated with unhealthy pregnancy outcomes, especially low birth weight babies, a new study finds.

Further, heavier weed use is associated with higher risks for the pregnancy, the researchers added.

"Cannabis use is not safe,"said senior researcher Dr. Robert Silver, a professor of obstetrics and gynecology at University of Utah Health. "It increases the risk of pregnancy complications. If possible, you shouldn't use cannabis during pregnancy."

In the past decade, the percentage of Americans using medical marijuana has more than doubled, and state-level recreational legalization has become increasingly common, researchers said in background notes.

Some previous studies have found no association between weed use and pregnancy complications, but those results have been inconclusive because there are "so many differences between baseline characteristics of people who use and don't use cannabis during pregnancy,"lead researcher Dr. Torri Metz, vice chair of research of obstetrics and gynecology at Utah, said in a university news release.

For example, there are different rates of anxiety and depression between pregnant women who use or don't use cannabis, and those differences can also impact pregnancy risk, Metz said.

For this study, researchers tracked the health of more than 9,000 women at eight medical centers across the United States.

About 610 had detectable levels of cannabis exposure, based on urine samples that provided a more accurate measurement of how much weed each woman had been using.

That allowed researchers to statistically untangle the effects of weed use from other factors like health conditions, smoking tobacco products, mood disorders and socioeconomic status.

Researchers looked at an aggregate measure of bad pregnancy outcomes, which included low birth weight, pregnancy-related high blood pressure, stillbirth and preterm birth.

Weed exposure was associated with a 1.5-fold increase in risk. About 26% of pregnant marijuana users experienced an unhealthy pregnancy outcome, compared with 17% of those who didn't use weed.

The association between weed use and low birth weight was the strongest, researchers said.

Also, higher levels of cannabis exposure over the course of pregnancy were associated with higher risks, researchers said.

The greater risk seen at higher levels is concerning given the high amount of THC -- weed's intoxicating chemical -- found in newer cannabis products, Silver said. These products were barely starting to become available from 2010 to 2014, when the study data was collected.

The findings were published Dec. 12 in the Journal of the American Medical Association.

Researchers speculate that long-term cannabis exposure might interfere with blood supply to the placenta, based on non-human primate studies. All of the pregnancy risks tracked in this study were also linked to reduced function of the placenta, which provides a growing fetus with oxygen and nutrients.

The research team urges people who are thinking about using weed during their pregnancy to talk with their doctor.

Pregnant women sometimes use weed to alleviate nausea or anxiety, but other remedies also are available that have been proven to be safe.

"There are many, many reasons people use cannabis,"Silver said. "But there may be alternative therapies that can help mitigate the symptoms."

More information

The U.S. Centers for Disease Control and Prevention has more on the health effects of marijuana during pregnancy.

SOURCE: University of Utah Health, news release, Dec. 12, 2023