More pregnant women are using marijuana now than a decade ago, and the rate is particularly high among younger pregnant women, according to a new analysis of survey data published in the Journal of the American Medical Association.

For the analysis, researchers from Columbia University combed through data from the National Survey on Drug Use and Health, focusing on more than 200,000 women from 18 to 44 years old. Among that group, 5.3 percent were pregnant at the time of the survey.

The rate of pregnant women who had used marijuana in the past month rose to 3.85 percent in 2014 from 2.37 percent in 2002. That’s an increase of 62 percent. Pregnant women between 18 and 25 years old had the highest use rate, with 7.47 percent of them using the drug within the past month.

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The researchers acknowledged that the overall prevalence of marijuana use during pregnancy is not very high, but said the increase should be studied further. The jump coincides with more states legalizing medical and recreational marijuana.

The risks of using marijuana while pregnant aren’t well understood. Some studies in people and animals have suggested that marijuana exposure during pregnancy might be associated with low birth weight and cognitive problems, but the evidence isn’t clear.

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Still, the American College of Obstetricians and Gynecologists recommends that women who are pregnant or are thinking about becoming pregnant avoid marijuana.