As marijuana use among U.S. adults doubled between 2011 and 2013 and 22 states legalized the drug for medical or recreational use, pregnant women are very much part of the trend, according to a new study.

National survey results published in the January 2017 issue of JAMA show that the percentage of pregnant women in the United States who had used marijuana in the past month increased from 2.37 percent in 2002 to 3.85 percent in 2014—equivalent to a 62 percent increase in use. Marijuana use was more prevalent among younger pregnant women, aged 18 to 25, with 7.47 percent reporting they had used the drug in the last month.

The percentage of pregnant women who used the drug in the past year also rose during this time, reaching 11.63 percent in 2014, according to the study, which included survey data from 200,510 women between the ages of 18 and 44. Deborah S. Hasin, Ph.D., a NARSAD 1989 Young Investigator, was the study’s senior author. Qiana L. Brown, Ph.D., MPH, LCSW, one of Dr. Hasin’s postdoctoral fellows from Columbia University, was lead author of the study.

Although the overall percentage of pregnant women using the drug is relatively low, physicians should be aware of rising rates of marijuana use, especially among younger pregnant patients, write Dr. Hasin and her colleagues, especially as “potential adverse consequences of prenatal marijuana exposure suggest further monitoring and research are warranted.”

In a comment published in the same issue of the journal, “The Risks of Marijuana Use During Pregnancy,” a team of researchers including National Institute on Drug Abuse Director Nora Volkow, M.D. discusses the current level of uncertainty about how marijuana may affect a developing fetus. Endocannabinoids, which are active substances in marijuana but also exist naturally in the human body, play an important role in early brain development, they write, and “substances that interfere with this system could affect fetal brain growth and structural and functional neurodevelopment.”

One potential cause for concern, according to Dr. Volkow, a BBRF Scientific Council member, and her colleagues, Drs. Wilson Compton and Eric Wargo, also of NIDA, is that pregnant women may use marijuana to control nausea, especially during early pregnancy when fetal brain development is at a critical stage. Given the uncertainty about marijuana’s effects of neurodevelopment, physicians should “err on the side of caution by not recommending this drug for their patients,” say Dr. Volkow and colleagues.