Marijuana use among adult pregnant women in the U.S. has been increasing, according to a new study published in the Journal of the American Medical Association.
Researchers at Kaiser Permanente’s Northern California Division of Research studied trends in prenatal marijuana use from 2009-2016, using data from more than 275,000 pregnant women who were being treated at one of the Kaiser Permanente health care facilities.
Early in their pregnancies, the women answered survey questions on their marijuana use, and also took a urine test.
Evaluating survey results over an eight-year period, the researchers noted that the number of women who reported smoking marijuana increased over time—especially among 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.
There was a subset of survey participants who denied using marijuana but had positive urine tests; researchers said they can’t tell whether those women had used the drug after realizing they were 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. Young-Wolff says changing marijuana usage patterns and attitudes toward the drug among the general population in California may have played a role in the results.
“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.”
The Kaiser Permanente parallels other research showing increasing marijuana use. From 2002 to 2014, self-reported, past-month marijuana use among pregnant women increased from 2.4 percent to 3.9 percent. In aggregated 2002-2012 data, 14.6 percent of U.S. pregnant adolescents reported past-month use.
In October, the American Congress of Obstetricians and Gynecologists issued an update to its committee opinion on marijuana use during pregnancy and while a woman is breastfeeding.
The committee declared that while most women believe that smoking marijuana is safe during pregnancy, it should be discouraged because scientists still don’t know exactly how it affects developing fetuses. There have not been enough studies done on the drug’s effects on pregnant women.
“The impacts of prenatal marijuana use haven’t been very well studied,” Young-Wolff 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 also be a factor; 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 factors that could have contributed to the increased risk.)
There is anecdotal evidence that some pregnant women may use marijuana to cope with the effects of morning sickness. But, “there are many other ways to treat nausea and vomiting during pregnancy,” Young-Wolff added.