A new report from the American Academy of Pediatrics (AAP) is cautioning pregnant women and nursing mothers to avoid marijuana due to possible adverse developmental affects in children.

The report, published recently in the journal Pediatrics, is also a call for more research into the effects of marijuana on fetal and child growth and development, and a warning about the reservations that have already been raised.

“I think we have enough emerging and consistent evidence that there is reason to be concerned about a fetus’ exposure to prenatal marijuana,” as well as infants’ exposure to “cannabis products from the mother,” said Sheryl A. Ryan, lead author of the report and a professor of pediatrics at Pennsylvania State University.

“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 Ryan, who is chair of the AAP’s committee on substance use and prevention. “But, in fact, there is still a big question. We do not have good safety data on prenatal exposure to marijuana.”

The appeal for caution also extends to nursing mothers who might consider using marijuana. Another article published in Pediatrics reports that THC, an intoxicating component of marijuana, not only crosses the placenta and enters the brain of a developing fetus, but also has been found to be present in breast milk up to six days after a mother’s last cannabis use.

That article also states that marijuana is the most commonly used illicit drug among breastfeeding women. According to the AAP, research statistics indicate that marijuana use among pregnant women has risen from 2.3 percent in 2002 to over 3.8 percent in 2014. Data from other studies suggest much higher percentages in some locations.

Both reports come when more states have made marijuana legal for recreational or medical use. Pennsylvania and New Jersey are among the states that allow marijuana to be used for certain medical purposes.

In addition, marijuana has become more potent, with average THC concentrations quadrupling since the 1980s.

Marijuana’s federal status as a highly restricted, illegal substance has limited the amount and scope of research conducted on the drug, including its potential benefits and adverse effects. The AAP report notes that the existing research into marijuana and fetal and child development has its critics. Nevertheless, the studies that have been conducted suggest links between prenatal exposure and possible neurodevelopmental effects. Those include harm to children’s executive function skills, such as attention, concentration, problem-solving, and impulse control.

Some research has suggested a higher risk of substance abuse disorder and mental illness among adolescents and adults who had prenatal exposure to marijuana.

“Many of these effects may not show up right away, but they can impact how well a child can maneuver in the world,” Penn State’s Ryan said. “Children’s and teens’ cognitive ability to manage their time and schoolwork might be harmed down the line from marijuana use during their mother’s pregnancy.”

Ryan said the hope is that more research will soon be conducted to confirm, clarify, or even put to rest some of these concerns. Pennsylvania, for example, has agreements with several universities to study the various therapeutic uses of marijuana.

But in the meantime, Ryan suggested that expectant and nursing mothers should side with caution and avoid substances that could have the potential to harm their unborn and newborn children.

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