Smoking weed during pregnancy leads to low birth weight, poor development, early delivery, death: study

A review of over 50 studies has found that the use of marijuana while pregnant leads to an increased risk of "adverse neonatal outcomes," including preterm births, low birth weight, developmental issues, death, and other effects.

The study was published in JAMA Pediatrics on Monday, and looked at 51 studies between November 1, 2021 and April 4, 2024. Overall, there were more than 21 million participants. 

The research found that there was a 52 percent higher risk of preterm delivery before 37 weeks with marijuana use during pregnancy, and a 75 percent increase in risk of low birth weights under around 5.5 lbs. The research noted that just six of the included studies looked at the impact of the drug on mortality, which found a 29 percent increase in risk of death to the infant. 

Dr. Jamie Lo, an associate professor of obstetrics, gynecology and urology in the School of Medicine at Oregon Health & Science University in Portland and lead author of the study told CNN, "The most striking finding is the increased risk of perinatal mortality — death either during the pregnancy or shortly after the pregnancy.”

“Prior work we’ve done shows prenatal cannabis use impacts fetal lung function and development, reducing the baby’s lung volume,” Lo said. “We’ve also found that there is significantly decreased blood flow and oxygen availability in the placenta. These are the likely underlying mechanisms driving some of our findings.”

The study noted that cannabis use by pregnant women has "more than doubled" in the past two decades, however, "clinicians are not consistently counseling patients regarding prenatal cannabis use, partly because of the limited and mixed available evidence."

"There is a mistaken perception that because marijuana is natural and plant-based, it’s not harmful," Lo said. "I remind my patients that opium and heroin are also plant-based. Tobacco is a plant, and alcohol is also made from plants."