Reviewed by Brunilda Nazario, MD on August 31, 2018

Aug. 31, 2018 -- Pregnant women with mild or severe morning sickness were significantly more likely to have used marijuana during pregnancy than women without these symptoms, according to a new study published this month.

The study of women in California found that a growing number of pregnant women are using marijuana, but those with severe nausea and vomiting in their first trimester were nearly four times more likely to use it during this time than those who didn’t have morning sickness.

The study of more than 220,000 pregnancies from 2009 through 2016 found overall use at 5.3% in the first trimester. That number spiked to 11.3% for pregnant women with severe nausea and vomiting. Just over 8% of the women with mild nausea and vomiting used pot while pregnant.

Women said on questionnaires that they used marijuana and were given a urine test when they were 8 weeks pregnant.

“Our findings add important evidence to a small but growing body of research suggesting that some pregnant women may use marijuana to self-medicate morning sickness,” said the study’s lead author, Kelly Young-Wolff, PhD, a research scientist with Kaiser Permanente’s Division of Research in Northern California.

The American College of Obstetricians and Gynecologists (ACOG) discourages women from using marijuana if they plan to get pregnant, are pregnant, or are breastfeeding.

In a statement responding to the study, the organization says “worrisome trends” in studies show that marijuana -- whether smoked or ingested -- may disrupt normal brain development in fetuses, resulting in shorter attention spans and behavioral problems in children. The CDC, too, says that while smoking marijuana transmits dangerous chemicals through the smoke, edible marijuana, found in brownies, candies, and other foods, is just as much of a problem.

Many women who use marijuana may think it’s relatively safe. But when smoked, it contains many of the same carcinogens as tobacco smoke, often in higher concentrations. The ACOG also warned that other issues may come from the increasing potency of marijuana, which is now legally sold for medicinal or recreational use in more than two dozen states, with more joining their ranks every year.

The association says previous studies have shown that children who were exposed to marijuana in their mother’s womb had lower scores on tests of visual problem solving, hand-eye coordination, and visual analysis than children who were not exposed to marijuana in utero. Prenatal marijuana exposure has been tied to attention deficit and behavioral problems. These children are also more likely to use marijuana as teenagers.

Young-Wolff said the perception that marijuana is harmless has been rising as more states legalize it. She cited a study done in Colorado that found that nearly 70% of marijuana dispensaries recommended marijuana to treat morning sickness.

“Just because it’s legal doesn’t mean that it’s safe, especially in pregnant women,” she says. “It’s important for people to realize that people who work in marijuana dispensaries are not medical professionals. We really recommend that pregnant women with nausea and vomiting talk to their doctors and don’t use marijuana.”

The study didn’t look at whether pregnant women smoked marijuana or ingested edibles.

“That’s something we hope to look at in the future,” she said.

Young-Wolff was one the writers of an editorial saying more data is needed on the health effects of marijuana use during pregnancy and on mothers and their children.

“An urgent need exists to understand the effects of prenatal marijuana exposure because it may continue to rise in conjunction with the growing acceptance, accessibility, and spread of legalization in the United States,” she wrote.

Show Sources

JAMA Internal Medicine: “Association of Nausea and Vomiting During Pregnancy With Prenatal Marijuana Use.”

American College of Obstetrics and Gynecology: “ACOG Committee Opinion: Marijuana Use During Pregnancy and Lactation.”

Jamilia Vernon, ACOG spokeswoman.

Kelly C. Young-Wolff, PhD, research scientist, Kaiser Permanente Northern California Division of Research, Oakland, CA.

Annals of Internal Medicine, Ideas and Opinions: “Data are Needed on the Potential Adverse Effects of Marijuana Use in Pregnancy.”

American Journal of Obstetrics and Gynecology: “Recommendations from Cannabis Dispensaries on First Trimester Marijuana Use.”


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