More pregnant mothers in California are lighting up than ever before, according to a study released Tuesday.

The study, from the Journal of the American Medical Association (JAMA), notes that from 2009 to 2016, pot use among expectant mothers jumped from 4.2 percent to 7.1 percent.

Some of the sharpest increases in marijuana usage were among pregnant women under the age of 18 and between the ages of 18 to 24 years old.

Pot usage among the women in the under-18 age bracket went up from 9.8 percent to 19 percent over the study period. For women in the 18 to 24 age bracket, marijuana usage spiked from 12.5 percent to 21.8 percent in that same period.

The study also reported an increase in pot usage among older pregnant women ages 25 to 34. Weed usage among women in that age bracket increased slightly, from 3.4 percent to 5.1 percent.

“Marijuana is [one of] the most commonly used illicit drugs during pregnancy, and its use is increasing,” the study says.

Researchers say the data comes from self-reported surveys that “likely underestimate use” of the drug.

Many pregnant women are turning to the drug to treat morning sickness or anxiety associated with pregnancy.

Not a lot of research has been done on how pot affects an unborn baby, but the Centers for Disease Control warns that pregnant women who light up risk having a child with a low birth weight and developmental issues.

The American Congress of Obstetricians and Gynecologists recommends that women who are pregnant, planning to become pregnant, or are breastfeeding should avoid the drug because the effects of marijuana on unborn and newborn children are not well known.

Despite the uncertainty of how the drug affects the body, California will legalize recreational marijuana for adults over the age of 21 beginning January 1.

Medical use of marijuana is already legal in California, which was one of the first states to legalize marijuana for that use two decades ago.