Two studies published this week in the medical journal JAMA are raising alarms about cannabis use during pregnancy.

One study by National Institutes of Health researchers shows an increase in the number of pregnant women who report cannabis use in the past month, which has doubled over the last 15 years. The other describes an elevated risk of preterm delivery among women who report cannabis use during pregnancy.

Taken together, the studies paint a concerning picture, says Dr. Michael Silverstein, a pediatrician at Boston Medical Center's Grayken Center for Addiction. He co-authored an editorial accompanying the two articles, called "Cannabis Use in Pregnancy: A Tale of 2 Concerns."

"The dialogue around cannabis use, at least to date, has really been defined as sort of a misperception of safety," Silverstein tells Here & Now. This new research "really provides data to refute that perception."

Weed is now legal in some form in 33 states, as well as the District of Columbia. And according to the American College of Obstetricians and Gynecologists, cannabis is the illicit drug most commonly used during pregnancy.

In 2003, just 3.4% of pregnant women told the National Survey on Drug Use and Health that they had used cannabis in the past month. By 2017, that statistic had jumped up to 7%.

But researchers don't know exactly what effect THC -- the psychoactive compound in cannabis — has on a fetus, as Kelly Young-Wolff, a researcher with Kaiser Permanente Northern California Division of Research, told Vox. Since there's not enough evidence to determine the risk, the American College of Obstetricians and Gynecologists discourages cannabis use during pregnancy.

"No amount of cannabis has been shown to be safe during pregnancy," Young-Wolff says.

Some research suggests that marijuana increases the risk of stillbirth and negatively affects children's visual-motor coordination, as NPR has reported. In her research, Young-Wolff found that pregnant women with severe nausea and vomiting had four times greater odds of cannabis use than other women — but she told Vox it's not clear if weed exacerbated their morning sickness or vice versa.

"There's a fairly widespread phenomenon of marketing of cannabis to pregnant women for morning sickness," Silverstein says, adding that it's not as simple as just telling expectant parents to stop smoking or find other solutions for their morning sickness.

He writes in his editorial about his second concern: how this preliminary research could shape an emerging dialogue around cannabis and pregnancy.

"The other important lesson in these studies is more a historical note," Silverstein says.

Early, flawed studies on in utero cocaine exposure opened the door for the medical community and the public to exaggerate the risks of cocaine in pregnancy, Silverstein explains. That exaggeration amplified racist "crack baby" stereotypes and did little to help combat urban poverty. Now he's worried how the cannabis conversation — and the judgement surrounding it -- might affect young people, especially those of color.

"It's easy to take these data and imbue them with judgment on women," Silverstein says. "And I would say we, as a lay community and as a medical and public health community, should really heed the lessons of past dialogues around alcohol, cocaine use and others."

More research is necessary, he says — not more judgment.

Francesca Paris produced this interview and edited it for broadcast with Tinku Ray, and adapted it for the web.