Marijuana use is on the rise in the United States as cannabis continues to gain acceptance. Now findings published in JAMA Network Open reveal an increase in the number of women who smoke weed in the year before they become pregnant and even early during their pregnancies, Kaiser Permanente reports.

For the study, researchers examined self-reported cannabis use among nearly 277,000 pregnant women from 2009 to 2017 using information from women’s initial prenatal visits at Kaiser Permanente in Northern California. Visits took place around the eighth week of pregnancy and did not reflect continued marijuana use throughout pregnancy.

In the year before pregnancy, cannabis use rose from 6.8% to 12.5% among women. In addition, self-reported cannabis use by women while they were expecting grew from 1.95% to 3.38%. Among those daily users who self-reported smoking pot during the year prior to becoming pregnant, scientists noted an increase from 17.1% to 25.2%, and weekly users jumped from 20.4% to 22%. (The proportion of women who used cannabis on a monthly or less than monthly basis declined from 62.7% to 53.1%.)

The number of women who self-reported smoking during pregnancy also increased. Daily users rose from 14.6% to 20.9% and weekly users from 25.1% to 27.4%. Monthly users decreased from 60.3% to 51.8%. (Investigators didn’t differentiate whether self-reported cannabis use during pregnancy occurred before or after women were aware that they were pregnant.)

Some women use cannabis during pregnancy to help manage morning sickness. Previous findings showed that women who experienced severe nausea and vomiting in pregnancy were nearly four times as likely to use marijuana during the first trimester of pregnancy. Furthermore, researchers believe the rise in daily and weekly cannabis use can be attributed to the legalization of recreational marijuana in California in 2018.

“Women may get the impression from cannabis product marketing and online media that cannabis use is safe during pregnancy,” observes Kelly Young-Wolff, PhD, MPH, a research scientist with the Kaiser Permanente Division of Research and lead author of the study. “However, there is substantial evidence that exposure to cannabis in pregnancy is associated with having a low-birth-weight 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.”

Other experts urge that more research is needed to better understand the effects of cannabis on pregnant women and their unborn children.

Until such research is available, Kaiser Permanente recommends that women stop cannabis use prior to conceiving and once their pregnancy is confirmed.

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