Number of women using cannabis before, during pregnancy on the rise, study says

The number of women using cannabis in the year before they get pregnant and early in their pregnancies is increasing, and their frequency of use is also rising, according to a new study by Kaiser Permanente in Oakland, California, and published in JAMA Open Network.

The research examined self-reported cannabis use among 276,991 pregnant women, representing 367,403 pregnancies, in Northern California over 9 years and found that cannabis use has increased over time.

From 2009 to 2017, the adjusted prevalence of self-reported cannabis use in the year before pregnancy increased from 6.8 percent to 12.5 percent, and the adjusted prevalence of self-reported cannabis use during pregnancy increased from 1.9 percent to 3.4 percent. Rates were adjusted for demographics. Annual rates of change in self-reported daily, weekly, and monthly-or-less cannabis use increased significantly, though daily use increased most rapidly.

Among women who self-reported cannabis use during the year before pregnancy, the proportion who were daily users increased from 17 percent to 25 percent, and weekly users increased from 20 percent to 22 percent, while monthly-or-less users decreased from 63 percent to 53 percent during the study period.

Similarly, among women who self-reported cannabis use during pregnancy, the proportion who were daily users increased from 15 percent to 21 percent, and weekly users from 25 percent to 27 percent, while monthly users decreased from 60 percent to 52 percent.

In addition, the prevalence of daily and weekly cannabis use may have risen even further in the past year and a half following legalization of cannabis for recreational use in California in 2018, according to Kelly Young-Wolff, PhD, MPH, lead author and a research scientist with the Kaiser Permanente Division of Research.

The data come from women's initial prenatal visits at Kaiser Permanente in Northern California, which usually take place at around  eight weeks gestation, and do not reflect continued use throughout pregnancy. Investigators were unable to differentiate whether self-reported cannabis use during pregnancy occurred before or after women were aware that they were pregnant, according to the study abstract.

While the current findings are based on women's self-reporting, the results are supported by the Kaiser Permanente research team's December 2017 JAMA Research Letter showing an increase in prenatal cannabis use via urine toxicology testing. In this newer study, which was supported by a grant from the National Institute on Drug Abuse, the authors focus on trends in frequency of use in the year before and during pregnancy.

Some women may use cannabis during pregnancy to manage morning sickness, the authors noted. The authors' previous work published in JAMA Internal Medicine in 2018 found women with severe nausea and vomiting in pregnancy were nearly 4 times more likely to use cannabis during the first trimester of pregnancy.

Women may get the impression from cannabis product marketing and online media that cannabis use is safe during pregnancy, said Young-Wolff. However, there is substantial evidence that exposure to cannabis in pregnancy is associated with having a low-birthweight baby, and the American College of Obstetricians and Gynecologists recommends women who are pregnant or contemplating pregnancy discontinue cannabis use because of concerns about impaired neurodevelopment and exposure to the adverse effects of smoking.

"These findings should alert women's health clinicians to be aware of potential increases in daily and weekly cannabis use among their patients," said lead author Kelly Young-Wolff, PhD, MPH, a research scientist with the Kaiser Permanente Division of Research. "The actual numbers are likely higher, as women may be unwilling to disclose their substance use to a medical professional."