Pediatricians are warning pregnant mothers to abstain from using marijuana during pregnancy and while breastfeeding.

Health experts are concerned after a new study from the American Academy of Pediatrics found that marijuana use among pregnant women increased by 62 percent between 2002 and 2014 in the U.S.

“The fact that marijuana is legal in many states may give the impression the drug is harmless during pregnancy, especially with stories swirling on social media about using it for nausea with morning sickness,” said Dr. Sheryl A. Ryan, one of the lead authors of the report and chair of the AAP Committee on Substance Use and Prevention, in a statement.

“But in fact, this is still a big question. We do not have good safety data on prenatal exposure to marijuana,” Ryan said. "Based on the limited data that does exist, as pediatricians, we believe there is cause to be concerned about how the drug will impact the long-term development of children."

Statistics found in the clinical report showed that "more babies than ever are being exposed to marijuana."

Thirty states, along with the District of Columbia, have passed laws allowing some form of marijuana use.

What were the findings?

The study found that Tetrahydrocannabinol, or THC, could be found in mother's breast milk up to six days after the mother last used the drug.

In pregnant women, "THC readily crosses the placenta and enters the rapidly developing brain of the fetus," according to the report.

There's not a lot of information available on what happens when the drug enters the fetus' system, but there's information suggesting "links between prenatal exposure and possible neurodevelopment effects."

“There’s still a lot we don’t know about how marijuana affects a baby’s rapidly developing brain,” Dr. Mary E. O’Connor, a co-author of the clinical report, said in the release. O'Connor is also an executive committee member of the AAP Section on Breastfeeding.

“But, based on what we know now, we’re advising women who are pregnant or nursing that the safest choice for their child is to avoid marijuana.”

The AAP has called for more research to learn about the possible developmental effects of THC on children.

What else?

THC levels in marijuana have in spiked over the last decade. It's much more potent than the pot smoked in the 1970s and 1980s.

The average potency is 20 percent but can be much higher. Concentrates may contain as much as 90 percent THC.