In 2014, nearly 4 percent of pregnant women said they'd recently used marijuana, up from 2.4 percent in 2002, according to an analysis of annual drug use surveys.
US women are increasingly using marijuana during pregnancy, sometimes to treat morning sickness, new reports suggest.
The trend has raised some concerns in the medical community, as doctors have warned that marijuana use during pregnancy can cause low birth weight, premature birth, and behavior problems in young children. Among that group, 5.3 percent were pregnant at the time of the survey.
Americans in general have been using more marijuana since 2001, according to the study, which was published today (Dec. 19) as a research letter in the journal JAMA.
Volkow noted that laws legalizing medical marijuana in 28 states and Washington, D.C.do not list pregnancy-related conditions among allowed uses.
The American College of Obstetricians and Gynecologists discourages marijuana use by women who are pregnant or breastfeeding.
Researchers found that 3.9 percent of pregnant women reported on a 2014 government survey that they had used marijuana during the past month, up from 2.4 percent who said the same on a 2002 survey, according to the study.
For nonpregnant women of reproductive age, the researchers found that the rates of past-month marijuana use also increased during the study period, from 6.3 percent in 2002 to 9.3 percent in 2014.
About 13 percent said they had used marijuana; that translates to about 30 million adults.
Dr. Marion P. Jarlenski from the University of Pittsburgh, Pennsylvania, who has studied public health messages about perinatal marijuana use, told Reuters Health by email, "One point that I would like to raise, as a public health policy researcher, is that women who use marijuana in pregnancy may face legal harms from state laws requiring physicians to report to child protective services fetuses or infants who are exposed to substances". The majority of users-90 percent-used it for nonmedical reasons only, and six percent used it only for medical reasons.