The National Institute on Drug Abuse says that some research shows that the effects of marijuana exposure could be long lasting, with marijuana-exposed children more likely to show gaps in problem-solving skills, memory, and the ability to remain focused.
In October, the American College of Obstetricians and Gynecologists (ACOG), which discourages marijuana use among pregnant or breastfeeding women, said that prenatal marijuana use could cause harm to an infant's brain development and function.
Participating women were asked to answer a questionnaire and go through a drug test to see if they tested positive for marijuana use.
The researchers found that the prevalence of marijuana use, based on self-reports or toxicology results, soared among all age groups, but the biggest rise was among those 24 and younger.
Worryingly, if women are not reporting their marijuana use in their medical records, their doctors are unable to counsel them about the risks of using marijuana, or what alternative reliefs for symptoms like nausea might be available.
One experts speculates that the rise might be partially explained by the increased availability of legal marijuana in recent years.
"Marijuana is the most commonly used illicit drug during pregnancy, and its use is increasing", the study said.
While studies on pregnant women who use marijuana have been limited, the researchers state that prenatal use of marijuana may impair fetal growth and neurodevelopment.
California became the first USA state to legalize medical marijuana in 1996.