More pregnant women seem to be using pot — sometimes to ease the nausea of morning sickness or heightened anxiety — and a new study suggests that this slight rise in marijuana use is most pronounced among those younger in age. The prevalence of marijuana use among a sample of moms-to-be in California climbed from 4.2% to 7.1% from 2009 through 2016, according to a research letter. Among pregnant teens younger than 18, marijuana use climbed from 12.5% to 21.8%, and among women 18 to 24, marijuana use climbed from 9.8% to 19%, the researchers found. That research involved only certain women in California, but 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% in 2002 to 3.85% in 2014. The women were 18 to 44.