"In aggregated 2002-2012 data, 14.6 percent of USA pregnant adolescents reported past-month use".
Marijuana use among pregnant mothers in California rose from 4.2 percent to 7.1 percent from 2009-2016.
Researchers observed a sample of pregnant women in California and saw a 3-percent increase in use form 2009 through 2016.
The letter said, "use among females younger than 18 years to age 24 years of age increased the most, from 12.5 percent to 21.8 percent for those younger than 18 years, and from 9.8 percent to 19 percent for those aged 18 to 24".
Worryingly, if women are not reporting their marijuana use in their medical records, their doctors are unable to counsel them about the risks of using marijuana, or what alternative reliefs for symptoms like nausea might be available. However, studies are limited to self-reported surveys and likely underestimate use due to social desirability bias and underreporting, leaving the scope of the problem unclear.
There's a new study out suggesting that more pregnant women appear to be using marijuana, sometimes to soothe anxiety and morning sickness.
On January 1, 2018, marijuana will become legal for recreational use in California, making it easier to buy for anyone over 21 there.
California became the first USA state to legalize medical marijuana in 1996.