Pregnant women who use marijuana may risk slowing the growth of the developing fetus, according to a Minnesota-based study released last week.
“Our study confirms what others have reported about potential risk,” said the study's lead author, Dr. Elyse Kharbanda of the HealthPartners Institute.
The study results come at a time when Gov. Tim Walz and some legislators are advocating that the state legalize recreational marijuana.
In a telephone interview, Kharbanda declined to take a position on whether that should occur.
“I just would caution that the information about risks not be lost as these conversations unfold,” she said.
The study, conducted by researchers at the University of Minnesota and the University of Iowa, as well as HealthPartners, looked at data from more than 3,400 women receiving prenatal care during a 21-month period in HealthPartners clinics. Routine urine testing showed that about 8% of the women had cannabis in their system while pregnant.
According to the study, babies born to those women were more likely to be “small for gestational age,” a measure that takes into account how far along the pregnancy was at birth and provides a more sophisticated measure than birth weight alone, Kharbanda said.
It also found that 9.1% of the babies exposed to cannabis during pregnancy had an abnormal developmental screening at 12 months, compared to 3.6% of babies not exposed to cannabis.
Kharbanda noted that both the American College of Obstetrics and Gynecology and the American Academy of Pediatrics recommend that pregnant women or those likely to become pregnant not use marijuana.
The National Organization for the Reform of Marijuana Laws agrees that “in general, pregnant women are recommended to stay away from all controlled substances,” deputy director Paul Amentano wrote in an email. But he cited a 2017 study published in Preventive Medicine that reported no “long-term or long-lasting meaningful differences” between children exposed to cannabis in the uterus and those who were not.
Nonetheless, that study, which was led by Dr. Katrina Mark of the University of Maryland, also advised that “decreasing or stopping use of all recreational drugs should be encouraged during pregnancy.”
In the study Kharbanda led, it wasn’t clear if the women using marijuana were continuing regular use from the past or using it as a means to ward off morning sickness, she said. For at least some of the women, the marijuana use may have occurred before they were aware of their pregnancy, she added.
But her group’s study refers to a 2017 finding in Colorado that the majority of cannabis dispensaries in that state were recommending it as a treatment for morning sickness.
Armentano noted that the THC in marijuana is “well-established” as an anti-nausea drug, but said the people dispensing the drug “ought not to be providing medical advice.”
The decision should be guided on “a case-by-case basis by a physician that has a well-established relationship with his/her patient,” he wrote.