Researchers warn: Marijuana use during pregnancy linked to increased risk of adverse birth outcomes

Prenatal exposure to marijuana significantly increases a baby's risk of premature birth, low birth weight and admission to the neonatal intensive care unit, although it does not increase the risk of birth defects or death within the first year, a new study shows.

A recent study published in the journal Addiction found that babies exposed to marijuana in the womb were more likely to be born prematurely, have lower birth weights, and require care in the neonatal intensive care unit (NICU) than babies who were not exposed to marijuana prenatally. The study also noted that these babies who were exposed to marijuana did not have a higher risk of birth defects or death in the first year, including sudden unexpected infant death.

Maryam Sorkhou, first author of the study, commented: "Cannabis use among women of childbearing age is increasing globally, and pregnant women are no exception. We know that THC, the main psychoactive ingredient in cannabis, can pass from the mother to the fetus through the placenta and bind to receptors in the fetal brain. Our study adds to this knowledge, showing that prenatal exposure to cannabis increases the risk of several adverse birth outcomes."

meta-analysis method

This meta-analysis (a synthesis of previous studies) brought together results from 57 previous studies involving a total of 12,901,376 infants, 102,835 of whom were exposed to cannabis.

Twenty of the studies measured the association between in utero cannabis exposure and risk of preterm birth. The combined results of these studies showed that mothers who smoked marijuana during pregnancy were more than one and a half times more likely to have a preterm birth than mothers who did not use marijuana during pregnancy.

Eighteen studies measured the risk of low birth weight. The combined results of these studies showed that mothers who smoked marijuana during pregnancy were more than twice as likely to have a low birth weight baby compared with mothers who did not use marijuana during pregnancy.

Ten studies measured the risk of needing neonatal intensive care unit admission. The combined results of these studies showed that newborns exposed to marijuana in utero were more than twice as likely to require admission to the neonatal intensive care unit as newborns not exposed to marijuana.

The studies included in this meta-analysis were published between 1984 and 2023 and involved multiple countries.