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Infants prenatally exposed to cannabis are more likely to be born preterm, have a low birth weight and require neonatal intensive care than infants without prenatal cannabis exposure, a new study by researchers at the Centre for Addiction and Mental Health (CAMH) and the University of Toronto has found. 

, the study also found cannabis-exposed infants are not at greater risk of birth defects or death within one year, including sudden unexpected infant death. 

“The global increase in cannabis use among women of reproductive age also extends to pregnant women,” says Maryam Sorkhou, a PhD student at U of T’s Temerty Faculty of Medicine’s Institute of Medical Science and lead author on the study. “We know that THC, the main psychoactive constituent in cannabis, can cross the placenta from mother to fetus and bind to receptors in the fetal brain.”

Sorkhou worked on the study with Tony George, a clinician-scientist at CAMH and a professor in the Temerty Faculty of Medicine’s department of psychiatry and Institute of Medical Science.

This study pooled the results of 57 prior studies from around the world. 

Those studies occurred from 1984 to 2023, and collectively included health outcomes of more than 12 million infants, including more than 102,000 infants exposed to cannabis before birth.   

For example, 20 of the studies included measured the association between intrauterine cannabis exposure and risk of preterm delivery.   

In these, the combined results show that mothers using cannabis were over one and a half times more likely to have a preterm delivery compared with mothers not using cannabis during pregnancy. 

Another 18 of the studies included also measured the risk of low birth weight.   

In these, the combined results show that mothers using cannabis during pregnancy were more than twice as likely to have a low-birth-weight baby compared with mothers not using cannabis during pregnancy. 

Ten of the studies included also measured the risk of requiring NICU admission.   

In these, the combined results show that newborns with intrauterine cannabis exposure were more than twice as likely to require NICU admission than non-exposed newborns. 

“Our study adds to that knowledge by showing that prenatal exposure to cannabis heightens the risk of several adverse birth outcomes,” Sorkhou says.