Using cannabis in early pregnancy could increase the risk of stillbirth and low birth weight, study suggests

The American Academy of Pediatrics recommends abstaining from using any cannabis products during pregnancy. Crystal Cox/Business Insider
  • A new study suggests cannabis use during pregnancy might increase the risk for stillbirths and preterm labor.
  • The study was limited because it could not fully isolate marijuana use from other factors that might contribute to health problems.
  • Still, the American Academy of Pediatrics does not recommend using cannabis during pregnancy.

Using cannabis even early on during pregnancy could impact the baby’s health at birth, a new study suggests.

The study, published on February 9 in the the American Journal of Obstetrics & Gynecology, compared people who used cannabis during early pregnancy to those who didn’t by analyzing health data and urine samples from about 9,000 women across the US.

Women who tested positive for marijuana within the first 14 weeks of pregnancy had a 27% likelihood of having babies with a low birth weight, stillbirth, preterm birth, and high blood pressure during pregnancy, compared to the 18% likelihood for these conditions among non-users.

Researchers measured those particular health problems because they are associated with complications during the formation of the placenta, the organ that delivers oxygen and nutrients to the fetus.

Dr. Torri Metz, an associate professor of obstetrics and gynecology at the University of Utah and the study’s lead author, told Insider her team grouped all of these complications together because they can occur simultaneously if the placenta does not function properly.

Metz said she was not surprised by the study’s findings, since prior research has associated marijuana use with abnormal fetal development.  “With this particular study, I think the question was if we really do universal testing on everyone to see if they have had cannabis exposure, maybe that result would be different,” Metz said. “Because a lot of the other studies just relied on clinical testing, which people worry is biased.”

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But there are very few quality studies that examine how marijuana use during pregnancy impacts the fetus or child’s health, according to Dr. Sheryl Ryan, a professor of pediatrics at Penn State Health who authored a clinical report on cannabis use during pregnancy. (Ryan was not involved in the study released on February 9.)

Earlier research has “postulated” that marijuana use during early pregnancy could impair the placenta’s function, but this data is “very limited,” Ryan said, in part because people who use cannabis may also smoke tobacco products — obscuring marijuana’s direct impact.

Ryan said a limitation of Metz’s study was that people who tested positive for marijuana tended to have other factors that affect pregnancy outcomes, like experiencing more stress, though Metz said her team adjusted the data to control for these differences.

Metz said, ideally, researchers would test how marijuana use impacts pregnancy using a randomized, double-blind trial — the “gold standard” for research — but asking a controlled group to use cannabis while pregnant would be “unethical,” she said, as it might inflict harm on an unborn baby. Cannabis is also illegal on a federal level, creating more barriers for research.

Despite limited research into the topic, Ryan said the American Academy of Pediatrics does not recommend pregnant people use cannabis.

“We suggest that women who are pregnant or considering becoming pregnant be educated about the potential negative effects of using marijuana, as well as other substances, on the developing fetus, and abstain from using any cannabis products during pregnancy,” Ryan said.

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