Cannabis: Pregnant Women Are Using More Marijuana, Posing Unknown Danger to Babies

The number of pregnant women who have smoked marijuana might be more than you think—at least in California.

A new study, published Tuesday in JAMA, asked more than 275,000 pregnant women who were being treated at one of the facilities in the the Kaiser Permanente Northern California system to fill out a survey. On the survey, which the women completed early in their pregnancy, were questions about marijuana use. The women also took a urine test. The researchers looked at data from eight years and found that the number of women who reported smoking marijuana increased over time—especially for mothers who were less than 18 years old at the time and for those who were between 18 and 24. In 2016, nearly a quarter of pregnant teenagers had used marijuana, as had about one in five women between 18 and 24. However, for those women who denied using marijuana but had a positive urine test, it’s impossible to tell if she had used the drug after she realized she was pregnant.

"That was not surprising, necessarily, but definitely concerning," Kelly C. Young-Wolff, one of the authors of the paper, told Newsweek. Young-Wolff is a licensed clinical psychologist and research scientist at the Kaiser Permanente Northern California Division of Research. Overall, marijuana use during the first weeks of pregnancy increased from about 4 to 7 percent between 2009 and 2016. Given that both the percentage of people reporting using marijuana and those whose urine tests showed they'd used it increased, more people may be using it in the general, non-pregnant population and marijuana use may be more accepted and normalized than ever before—again, at least in California.

"California is a little different in that we were the first state to legalize medical marijuana in 1996," Young-Wolff said. "Our data might be very different if you looked in another state. But California does tend to be a leader in terms of trends, and it may be indicative of what will be happening in other states in the future."

Japan babies crawling Babies compete in a baby crawling competition hosted by a Japanese magazine on November 23, 2015. The competition was held to challenge the Guinness World Record for the largest crawling competition with the maximum number of participants. KAZUHIRO NOGI/AFP/Getty Images

In October, the American Congress of Obstetricians and Gynecologists put out an update to its committee opinion on marijuana use during pregnancy and while a woman is breastfeeding. (This kind of document is just an opinion based on the scientific evidence that’s available—it doesn’t lay out rules that OB-GYNs have to follow.)

The committee opinion stated that while most women believe that smoking marijuana is safe during pregnancy, it should be discouraged because scientists still don’t know exactly what it does to developing fetuses. Good studies on the actual effects just don’t exist yet. "The impacts of prenatal marijuana use haven't been very well studied," Young-Wolff said. Beyond birth weight, she said, "data are really limited by the number and the quality of existing studies. Definitely, more research is needed." 

There are, however, “worrisome trends,” the committee wrote. “The effects of marijuana use may be as serious as those of cigarette smoking or alcohol consumption.”

Those effects include lower birth weights for the children of mothers who use a lot of pot, for example. Timing may be important, too; marijuana use in the first month of a pregnancy may increase the likelihood of a very rare birth defect called anencephaly. (However, the committee opinion notes, there may have been other confounding factors that could have contributed to the increased risk.)

The number reported in the JAMA paper falls outside the range that’s been reported in other studies using self-reported data—between 2 and 5 percent. However, self-reported data is notoriously unreliable. (The percentage of women who tested positive for marijuana use in this paper was quite a bit higher than those who had just said they did.) Presumably, women may have been reticent to report smoking marijuana if they actually did because they might not want to seem like they’ve done something that people believe might put their child at risk. Urine tests, which are more reliable, also have their limitations; marijuana can linger in a person's urine about 30 days—and even longer for those just light up more than every once in a while. "It does vary quite a bit, which makes it tricky," Young-Wolff said. The potency of the pot can also affect the results. 

And women may even be using marijuana after they took the survey—on purpose. Anecdotally, Young-Wolff said, some women may take marijuana while they're pregnant to deal with morning sickness. However, she added, "there are many other ways to treat nausea and vomiting during pregnancy."