Researchers observed a sample of pregnant women in California and saw a 3-percent increase in use form 2009 through 2016.
"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.
More than one-fifth of American teenagers are using marijuana during pregnancy, a new study finds.
"Earlier broadly illustrative investigations have discovered that the commonness of cannabis use among US grown-up pregnant ladies has expanded after some time; in any case, these investigations have excluded target measures of biochemically checked pot utilize and likely think little of the commonness", said lead examine creator Kelly Young and senior creator Dr. Nancy Goler, both of Kaiser Permanente Northern California in Oakland.
At the same time, the American Congress of Obstetricians and Gynecologists released a statement in October, noting that "women who are pregnant or contemplating pregnancy should be encouraged to discontinue marijuana use" and "to discontinue use of marijuana for medicinal purposes in favor of an alternative therapy".
However, the study notes that some of the patients who did not say they used marijuana on their questionnaires, later tested positive on a cannabis toxicology test, leading researchers to state their data was "likely" underreported.
The study analyzed data from 280,000, gathered from 2009 to 2016.
However, the institute says more research must be done to determine which effects are related to marijuana exposure and which are related to environmental factors that could be associated with the mother's marijuana use, such as poverty or other drug use.
Experts believe that the use of marijuana could potentially harm a fetus's brain development, cognition and birth weight, The New York Times noted, and its main psychoactive ingredient, tetrahydrocannabinol (THC), could be transferred to a baby via breast milk.
While the letter does not discuss any potential problems from pot use during pregnancy, the Centers for Disease Control and Prevention (CDC) advises pregnant women to avoid it.
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.
Barbara Yankey, a researcher at Georgia State University, told Reuters marijuana use may be on the rise because of the recent legalization of its recreational use "has made people think of the drug as less risky, even during pregnancy". However, on a federal level, it is still illegal to possess, use, buy, sell, or cultivate marijuana.