Marijuana use among pregnant women is linked to low birth weight, study finds

It’s long been proven that smoking cigarettes is harmful to fetuses, and now a new study has confirmed that the use of cannabis during pregnancy — including medical marijuana — can increase health risks for babies.

Researchers from the University of Utah Health studied more than 9,000 pregnant women across the U.S., finding that marijuana use was linked with low birth weight, along with other poor outcomes.

The study was published in the Journal of the American Medical Association (JAMA) on Dec. 12.

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Dr. Torri Metz, vice chair of research of obstetrics and gynecology at Utah Health and lead author on the study, noted that there is increasing evidence that cannabis is linked to smaller babies. 

“The placenta is responsible for providing fetal nutrients and oxygenation, and is largely responsible for fetal growth,” she said in an email to Fox News Digital.

“So it was not very surprising to us that we also saw a higher rate of poor pregnancy outcomes that are related to how the placenta functions with cannabis exposure in this study.”

In the study, “poor pregnancy outcomes” consisted of stillbirth, preterm birth for a medical indication, high blood pressure in pregnancy and a baby who was small at the time of birth. 

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“We also found that there was more risk of these adverse outcomes with higher levels of cannabis use and ongoing use across the pregnancy,” Metz added.

Out of the more than 9,000 participants, who came from eight different medical centers across the U.S., 610 had “detectable levels of cannabis exposure.” 

The data was collected between 2010 and 2014.

The subset of pregnant women who were exposed to cannabis were shown to have a 1.3-times higher risk of delivering babies with low birth weight and other fetal health issues.

Cannabis levels were obtained via urine samples that measured a “metabolic byproduct of cannabis,” which resulted in a higher level of accuracy.

“Clinicians should continue to recommend against cannabis use in pregnancy by having a conversation with patients about the potential risks and safe alternatives to treat conditions.”

One potential reason for the negative outcomes is that cannabis may impede the flow of blood to the placenta, the researchers suggested.

Based on the findings, the researchers said pregnant women should consult with their doctor before using medical marijuana and consider safer options.

“This adds to what we know about cannabis use and pregnancy and demonstrates that there is concern for risks with use in pregnancy,” Metz told Fox News Digital. 

“Clinicians should continue to recommend against cannabis use in pregnancy by having a conversation with patients about the potential risks and safe alternatives to treat conditions.”

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The lead author said she hopes this “will also encourage” those who are pregnant “to discuss their cannabis use with their health care provider and to stop using prior to getting pregnant.”

One potential limitation of the study is that the researchers were not able to adequately examine some of the rare outcomes, like stillbirth, because they did not have a large enough population, Metz noted. 

“We also do not know how participants were using cannabis or what specific products they were using,” she added.

Dr. Courtney Boyle, OBGYN and medical director of the Connections Clinic at Lehigh Valley Health Network in Pennsylvania, was not involved in the Utah Health study but shared her comments on the use of cannabis during pregnancy.

“This study furthers our understanding of how marijuana use during pregnancy may lead to health complications for the fetus,” she told Fox News Digital. 

“As medical marijuana becomes more mainstream, we are seeing an increase in pregnant patients who desire to continue during their pregnancy, which is why studies like these are important.”

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When Boyle meets with patients who are using medical marijuana, she presents alternative treatments for them to consider.

“For patients who continue marijuana during the pregnancy, we counsel about the limited data on long-term effects, particularly with the newer products available.”

The American College of Obstetricians and Gynecologists (ACOG) recommends that anyone who is pregnant, planning to get pregnant or is breastfeeding abstain from marijuana use because of the limited scientific knowledge on the harms of this drug during pregnancy, Boyle pointed out. 

Risks to the fetus include “being small for gestational age, risk of preterm labor and neurodevelopmental effects long term,” she said.

Cannabis use can also have potential effects on the pregnant woman, the doctor noted, including permanent lung injury and dizziness, which raises the risk of falls. 

“Patients are offered referrals for drug and alcohol counseling should they desire,” said Boyle. 

“I would highly encourage pregnant women to have an open conversation with their health care providers to find ways to reduce potential health complications for their fetus.”

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