Marijuana Use While Pregnant Linked to Preterm Birth, Low Birth Weight

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Medically reviewed by Carmen Pope, BPharm. Last updated on May 6, 2025.

By I. Edwards HealthDay Reporter

TUESDAY, May 6, 2025 — Using marijuana while pregnant can harm a developing fetus in serious ways, new research shows.

A large review of 51 studies linked marijuana use during pregnancy to an increased risk of early delivery, low birth weight and even death. The review — published May 5 in JAMA Pediatrics — included more than 21 million participants.

“The most striking finding is the increased risk of perinatal mortality — death either during the pregnancy or shortly after the pregnancy,” lead study author Dr. Jamie Lo, an obstetrician at Oregon Health & Science University in Portland, said in a CNN report.

“We’ve also found that there is significantly decreased blood flow and oxygen availability in the placenta," she added.

The placenta supplies oxygen and nutrients to the fetus. When it doesn't work well, the fetus may not grow properly.

Earlier research by Lo showed that marijuana use can reduce the fetus's lung size and blood flow in the womb, too.

Despite the risks, marijuana use during pregnancy is on the rise. A 2019 study of more than 450,000 pregnant American women found it more than doubled between 2002 and 2017, especially in the first trimester. Most of that use was recreational, not medical, CNN reported.

“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.”

Lo also noted that researchers can never run clinical trials on pregnant women to test cannabis directly — that would be unethical. Instead, researchers study data from women who report using marijuana while pregnant.

The new study found that marijuana use during pregnancy was linked to:

  • A 52% higher risk of preterm birth (before 37 weeks)

  • A 75% higher risk of low birth weight (under 5.5 pounds)

  • A 29% higher risk of infant death

    • Despite obstacles, the quality of the research is improving, however.

    Just a year ago, Lo's team rated the science on cannabis and pregnancy as very low. Newer studies are stronger, leading to more confidence in the results, the CNN report said.

    “Research is evolving quickly in this area,” said Brianna Moore, an assistant professor of epidemiology at the Colorado School of Public Health Anschutz Medical Campus in Aurora.

    “This review found that as more studies are conducted with consistent results, there is more certainty that there is an association between prenatal exposure to cannabis and adverse birth outcomes," she added.

    But many parents and doctors see the messages as mixed.

    “Perceptions of safety are compounded by the increased availability and legalization of cannabis,” Lo said. “In addition, health care providers are poor at counseling due to confusion over conflicting studies. We’re trying to change that.”

    Experts also warn that today's marijuana is much stronger than in past decades, posing risks not reflected in earlier research.

    The bottom line?

    “Ideally, it’s best not to be exposed to THC, which is the psychoactive ingredient of cannabis, no matter what form you’re using,” Lo said.

    Sources

  • CNN, May 5, 2025

    • Disclaimer: Statistical data in medical articles provide general trends and do not pertain to individuals. Individual factors can vary greatly. Always seek personalized medical advice for individual healthcare decisions.

    Source: HealthDay

    Posted : 2025-05-07 06:00

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