Marijuana use among pregnant mothers in California rose from 4.2 percent to 7.1 percent from 2009-2016. Younger mothers-to-be were more likely to smoke marijuana. For pregnant teens under 18, marijuana use climbed from 12.5 percent to 21.8 percent. Among women 18-24, marijuana use climbed from 9.8 percent to 19 percent.
The research published Tuesday involved only certain women in California, according to CNN.
A separate study of pregnant women across the United States, published in JAMA in January, found that those who reported using marijuana in the previous month grew from 2.37 percent in 2002 to 3.85 percent in 2014. The women were 18-44.
The U.S. Centers for Disease Control and Prevention says the health effects of marijuana on a fetus could include low birth weight and developmental problems, according to CNN.