A study from 2015, published in American Journal of Obstetrics and Gynecology, found that marijuana freely crosses the placenta and is found in breast milk. This trend mirrors what's going on in society at large: In just the last few years, regulations and attitudes toward marijuana have undergone a seismic transformation.
According to Dr. Navizadeh, it is hard to determine the exact effects of marijuana use on babies and fetuses because, oftentimes, expectant mothers who are using marijuana may also be using other drugs.
In 2016, 7% of pregnant women in a California study tested positive for marijuana use, which is almost double the 4% who were using it in 2009.
It was also discovered that pot-use among girls under 18 in the coastal state increased as well, climbing from 9.8 percent to 19 percent.
"Use among [pregnant] females younger than 18 to age 24 years increased the most", added the team led by Kelly Young-Wolff, a Kaiser researcher in Oakland.
In women older than 34, marijuana use increased from about 2 percent to about 3 percent.
The study tested more than 30,000 women during each year of the eight-year study, using questionnaires and analyzing urine toxicology tests.
"California is a little different in that we were the first state to legalize medical marijuana in 1996", Young-Wolff told Newsweek.
While pot may be growing more popular, the science and statistics show a clear reasons why expecting moms need to think twice before choosing to use the drug.
The women who were asked to complete the study were in the early part of their pregnancy.
Rates of use were highest among the young, and dropped steadily as age rose during pregnancy, the researchers said. The American Congress of Obstetricians and Gynecologists updated a document that represents the organization's opinion on pressing matters titled the ACOG Committee Opinion.
Doctors caution pregnant women who use pot saying the health effects on fetuses remain unclear but include low birth weight and developmental problems.
Given how many pregnant women seem to be using pot, there's clearly a lot of confusion about its safety.
According to the National Institute on Drug Abuse (NIDA), more research is needed on the effects of marijuana use on developing babies. As Volkow points out, THC, which can make its way past a woman's placenta, does interact with the human body's brain development, and it's not a great idea to introduce it in utero.
Morning sickness affects a significant percentage of pregnant women. "We recommend (pregnant women) stop immediately". A 2012 study of pregnant women in Brisbane, Australia published in Pediatric Research found that, on average, babies born to women who reported smoking weed during pregnancy were about 375 grams lighter than babies born to women who didn't smoke while pregnant.