Infants born to mothers who used marijuana during pregnancy were twice as likely to be underweight and nearly twice as likely to be premature than infants who were not exposed to cannabis, a new study found.
Cannabis-exposed infants were 2.5 times as likely to be admitted to a neonatal intensive care unit, compared with unexposed babies, according to the study.
“We know that THC (tetrahydrocannabinol), the main psychoactive constituent in cannabis, can cross the placenta from mother to fetus and bind to receptors in the fetal brain,” said first author Maryam Sorkhou, a postdoctoral student at the University of Toronto, in a statement.
“Our study adds to that knowledge by showing that prenatal exposure to cannabis heightens the risk of several adverse birth outcomes.”
Marijuana use in pregnancy on rise
Use of marijuana by pregnant women has been growing in the United States and other countries such as Canada in recent decades. A 2019 analysis of over 450,000 pregnant American women ages 12 to 44 by the National Institute on Drug Abuse found cannabis use more than doubled between 2002 and 2017.
The vast majority of marijuana use was during the first three months of pregnancy, the study found, and it was predominantly recreational rather than medical.
Yet the first trimester may be one of the most sensitive times for the developing brain of a fetus, when it’s most susceptible to damage. Not only does THC – the compound in marijuana that makes you high – enter the fetal brain from the mother’s bloodstream, but once there it can affect the baby’s developing brain.
Studies have found receptors for cannabis in the brains of animals as early as five and six weeks of gestational age.
Past studies have shown the use of marijuana during pregnancy is linked to low birth weight, impulsivity, hyperactivity, attention issues and other cognitive and behavioral issues in children, according to the US Centers for Disease Control and Prevention.
There’s even a connection to autism. A 2020 study found that women who used weed during pregnancy were 1.5 times more likely to have a child with autism.
Over 100,000 infants exposed to marijuana
The new review, which published Thursday in the journal Addiction, analyzed 57 studies with a total of nearly 13 million infant participants — over 100,000 of those babies had been exposed to cannabis while in the womb.
There was good news: The study did not find an increased risk of birth defects due to cannabis use. Nor did it find a link between marijuana exposure in the womb and death within a year, including sudden unexpected infant death, or SIDS.
However, mothers using marijuana during pregnancy were 2.6 times more likely to give birth to a baby with a low birth weight, which can contribute to difficulties in eating, gaining weight and fighting infection.
“Low birth weight is one of the strongest predictors of a child’s health and development long-term,” Beth Bailey, professor of psychology and director of population health research at Central Michigan University’s College of Medicine in Mount Pleasant, told CNN in May.
“These kids are more prone to developmental delays, higher rates of ADHD (attention deficit hyperactivity disorder), learning disabilities, and have higher rates of emotional problems,” she said.
In fact, the meta-analysis found babies who were exposed in the womb had poorer attention spans and more problems with behavior in infancy and early childhood.
In addition, mothers using cannabis were 1.7 times more likely to spontaneously deliver their newborn prematurely in comparison with mothers without cannabis use, according to the study.
Premature infants can have issues with breathing and suffer a lack of development in the heart, lungs, brain, metabolism, digestive and immune systems. Indeed, the study also found that infants born to moms using marijuana were 2.5 times more likely to need to be admitted for intensive care.
A warning for pregnant people
Any woman using marijuana who discovers she is pregnant should immediately discuss the issue with her doctors, experts say.
The American College of Obstetricians and Gynecologists has this warning on its website: “Because of concerns regarding impaired neurodevelopment, as well as maternal and fetal exposure to the adverse effects of smoking, women who are pregnant or contemplating pregnancy should be encouraged to discontinue marijuana use.”
Yet many young women aren’t honest about their use, studies have shown. One study of women 24 years old and younger found they were about twice as likely to screen positive for marijuana use than they stated in self-reports.
