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SALT LAKE CITY — Higher exposure to cannabis during pregnancy is associated with more frequent unhealthy pregnancy outcomes, Utah researchers say.
Due to contradictory findings in studies on the health impacts of cannabis use while pregnant, researchers at University of Utah Health decided to conduct a much larger study to more accurately measure cannabis exposure and its effects. More than 9,000 pregnant women across the U.S. participated in the study.
"There's so much information out there — discussion and social media channels and on the internet — about cannabis use and pregnancy," Torri Metz, lead author of the study, said in a news release. "I think it's hard for patients to understand what they should be worried about, if anything."
Participants in the study gave three urine samples throughout their pregnancy, and the researchers then measured the level of metabolic byproduct of cannabis. This was to collect a more accurate measurement of cannabis exposure, compared to other studies where participants just reported cannabis use, researchers said.
The results, published in the Journal of the American Medical Association, show higher cannabis exposure throughout pregnancy is associated with higher rates of low birth weight, medically indicated preterm birth, stillbirth and pregnancy-related high blood pressure.
Of the 610 participants exposed to cannabis, about 25% had adverse pregnancy outcomes. That's compared to approximately 17% of the more than 8,500 participants not exposed to cannabis who also experienced negative outcomes.
Cannabis use had the strongest association with low birth weight, but all conditions of negative health outcomes were linked to reduced function of the placenta. Previous studies on primates found long-term cannabis exposure can interfere with blood supply to the placenta, and U. Health's study seems to suggest the same effect occurs in humans.
"Cannabis use is not safe," obstetrics and gynecology professor Robert Silver said in the release. "It increases the risk of pregnancy complications. If possible, you shouldn't use cannabis during pregnancy."
Metz said a problem the researchers faced was distinguishing consequences specifically from cannabis use versus those stemming from other factors. She said there are different characteristics between people who use and don't use cannabis during pregnancy, including rates of anxiety and depression, and so other factors can also contribute to pregnancy risks.
To address this, the researchers purposefully used a large study population with participants from eight medical centers across the country.
"Being able to compare pregnancy outcomes for so many participants, 610 of which had detectable levels of cannabis exposure, meant that the researchers could statistically untangle the impacts of cannabis use from many other factors, including pre-existing health conditions, nicotine exposure and socioeconomic status," the news release says.
After the impacts of other factors were removed, the researchers discovered cannabis exposure was associated with a 1.3-fold increase in risk; higher levels of exposure made that risk number even more, researchers said.
The risk for an adverse outcome was also found to be higher among those who continued to use cannabis beyond the first trimester, the study says.
Silver voiced concern that newer cannabis products have increased in the amount of THC, and the health impacts of more concentrated products are unknown. Further research needs to be done, he said, and urged those considering using cannabis while pregnant to talk to their doctor to find potential alternatives.
"As long as humans are interested in using this product, we ought to assess health effects both good and bad, as accurately as we can, and provide that information for folks," Silver said.
