Using marijuana during pregnancy is associated with serious risks, including poor fetal development, low birth weight, preterm birth, and even infant death, according to a new meta-analysis published in JAMA Pediatrics.
The study, led by Dr. Jamie Lo, an obstetrician at Oregon Health & Science University, analyzed data from 51 studies encompassing more than 21 million pregnancies. “The most striking finding is the increased risk of perinatal mortality,” Dr. Lo said, referring to deaths occurring during or shortly after pregnancy.
Marijuana’s Impact on Fetal Development
Cannabis use during pregnancy has been shown to affect fetal lung development and reduce blood flow in the placenta, which is vital for delivering oxygen and nutrients. This can result in reduced lung capacity and impaired growth in unborn babies.
Among the most alarming outcomes, the meta-analysis found:
- A 52% higher risk of preterm birth (before 37 weeks gestation).
- A 75% increased risk of low birth weight (under 5.5 pounds).
- A 29% higher likelihood of infant death, based on data from six specific studies.
The researchers used the GRADE system to assess the quality of the evidence. While earlier studies were rated as having low certainty, this review found that more recent data offers low to moderate certainty, showing improvements in research quality over time. Brianna Moore, a researcher at the Colorado School of Public Health, supported these updated findings.
Rising Use Despite Known Risks
Despite growing evidence of harm, marijuana use among pregnant women is on the rise. A 2019 study revealed that cannabis use more than doubled between 2002 and 2017 among American women aged 12 to 44. Most use occurs in the first trimester and is typically recreational, not medically advised.
Dr. Lo attributes part of the problem to common misconceptions. “People think marijuana is safe because it’s natural,” she said. “But so are opium and heroin. Even alcohol and tobacco are derived from plants, yet we know they can seriously harm a fetus.”
Risks from Other Substances
Like cannabis, other substances also pose well-documented dangers during pregnancy:
- Alcohol can cause fetal alcohol syndrome.
- Tobacco harms fetal brain and lung development.
- Opioids, such as heroin and fentanyl, are linked to birth defects and stillbirth.
Due to ethical concerns, researchers cannot conduct randomized clinical trials involving harmful substances in pregnant women. As a result, much of the available data comes from self-reported use by mothers, making robust meta-analyses like this one crucial for understanding risks.
Confusion Around Cannabis Safety
With marijuana increasingly legalized and socially accepted, expectant parents often receive mixed messages about its safety. Dr. Lo pointed out that even healthcare providers struggle to counsel patients amid conflicting studies and evolving cannabis products.
“There’s no clear public health messaging,” she said, adding that efforts are underway to create updated reviews and clinician guidelines for more consistent advice.
Adding to the confusion is the fact that much of the past research was based on lower-potency cannabis from the 1980s. Today’s products are often far more potent, which may intensify health risks.
Broader Health Concerns
Beyond pregnancy-related outcomes, marijuana use has been linked to a wide range of serious health problems:
- A 42% higher risk of stroke and 25% higher risk of heart attack, even in non-smokers.
- Heart issues, including arrhythmias and myocarditis (heart muscle inflammation).
- Mental health disorders, such as depression and anxiety, especially among younger users.
- Cognitive and behavioral issues in children born to cannabis users, including attention problems and psychotic-like symptoms.
- Cannabinoid hyperemesis syndrome, a condition causing severe vomiting from chronic use.
The CDC and other health agencies have also linked regular marijuana use with increased emergency care visits, complications during surgery, and even potential cancer risks.
“Ideally, it’s best not to be exposed to THC at all during pregnancy,” Dr. Lo advised, referring to the psychoactive component in cannabis.
