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Warnings against drinking alcohol and smoking cigarettes while pregnant are everywhere, but scientists — including some from UNLV — are just catching up on the consequences of a prospective mother using marijuana.

In a study published this fall in The Journal of Maternal-Fetal and Neonatal Medicine, researchers reviewed the sonogram data of 450 pregnant women who reported smoking marijuana daily. The study shows a link between marijuana use while pregnant and delayed fetal growth, which in extreme cases can lead to a stillbirth.

"Recent data from JAMA (The Journal of the American Medical Association) indicates that marijuana use in pregnancy has doubled over the last 15 years and what's more alarming is that 70 percent of women believe there is minimal or no harm from using marijuana in pregnancy,” Dr. Bobby Brar of the UNLV School of Medicine, one of the two lead authors of the study, said in a press release. "Our findings contribute to the growing body of evidence that fetal marijuana exposure may not be as safe as people think."

A woman’s daily use of marijuana while pregnant was shown to cause multiple health problems for her infant, such as an increased risk of low birth weight, low resistance to infections, and decreased oxygen levels.

One of the key findings of the study found that there was an increase in placental vascular resistance in the second and third trimesters — in other words, the flow of oxygen through the placenta is disrupted and leads to delayed growth.

“Anecdotally speaking, many of my patients tell me that they don’t think that there’s anything wrong with smoking marijuana in pregnancy and they’re not aware of any risks that are present to the fetus,” said Brar in an interview with The Nevada Independent. “There’s been a prior study that shows that 70 percent of women believed that there’s either minimal or no harm from using marijuana in pregnancy.” 

One reason there is little to no information on the risks of marijuana during pregnancy is the fact that it is illegal on a federal level. Many types of studies use federal funds and grants to conduct research and that funding is not available when you work with an illegal substance. 

“I would advise that all pregnant patients abstain from using any amount of marijuana in pregnancy,” Brar said. “Our recommendation is always that there is no known safe amount of alcohol exposure in pregnancy and I tend to have that same approach when it comes to cigarette smoke and now when it comes to marijuana, the only difference is that we’re still learning about what the extent of that marijuana might be.”

According to the report, an estimated 16 percent of pregnant women engage in daily marijuana use. 

“I do think that given how much [is] sort of unknown with regards to marijuana use on long term health, specifically in our field, ‘house of the fetus,’ I think that this is an area that we’re going to see more and more research in,” Brar said. “I think, and I hope over the next 10 to 20 years that we’re able to fully elucidate the effect of marijuana, not only on the fetus in utero but also at five to 10 years of age.”

The study was a retrospective cohort study where self-identified daily marijuana users who were pregnant were compared to control subjects. The study focused on comparing maternal demographics, fetal biometry, and umbilical artery dopplers, which measure the blood flow through the umbilical cord. 

With decades of evidence from the effects of smoking tobacco while pregnant, the Center for Disease Control and Prevention (CDC) warns of health risks such as birth defects, preterm birth, and an increased risk of sudden infant death syndrome (SIDS) if a mother smokes. There have been many campaigns to educate pregnant women about the dangers of tobacco, including warnings on cigarette cartons and helplines for quitting smoking. 

Just as with cigarettes, alcohol use while pregnant has also been widely studied and found to be dangerous for infants and mothers alike. Warnings on alcohol containers and in restaurants inform women about the dangers of drinking while pregnant. 

With recreational marijuana legal in 11 states and medical marijuana legal in 33, more research into the effects of cannabis is expected. And awareness campaigns are already underway: In Nevada and California, there are billboards along roadsides with the warning “Just because it is legal doesn’t mean it’s safe.” 

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