Health experts have been telling women for decades that it’s harmful to their unborn babies to smoke during pregnancy.

Approximately 12 to 20 percent of pregnant women still do, putting themselves and their babies at risk. Countless babies are born at low birth weights, preterm, or with a host of other health issues related to their mothers’ smoking habits — and more than 1,000 babies in the U.S. die each year as a result.

Does it matter if it’s a cigarette or a joint?

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Women of childbearing age may believe that if it’s marijuana they’re smoking, the risks don’t apply: Pot use among pregnant women has shot up 62 percent since 2002. And that number may be outdated — data right now is only available through 2014.

Related: Our Littlest, Most Vulnerable Ones are Going to Pot 

A new study released Monday in JAMA shows that 3.9 percent of pregnant women reported on a 2014 government survey that they’d used marijuana during the past month. That’s up from the 2.4 percent who said the same on a 2002 survey.

Babies born to women who used marijuana during pregnancy are more likely to be anemic and have lower birth weights, for starters.

While 3.9 percent may not seem all that significant a number, researchers from Columbia University’s Mailman School of Public Health in New York City said “the increases over time and potential adverse consequences of prenatal marijuana exposure suggest further monitoring and research are warranted.”

Americans in general have been using more marijuana since 2001, according to the study. Between 2001 and 2013, use has more than doubled among all adults. Counseling for marijuana use and screening, the authors note, is recommended for all women both pregnant and contemplating pregnancy.

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It is especially important, said Dr. Nora Volkow in an editorial accompanying the study, because more women are being told that marijuana might help them with nausea during early pregnancy.

“Some data suggest this population is turning to marijuana for its antiemetic properties, particularly during the first trimester of pregnancy, which is the period of greatest risk for the deleterious effects of drug exposure to the fetus. Marijuana is the most widely used illicit drug during pregnancy, and its use is increasing,” said Volkow, director of the National Institute on Drug Abuse.

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Babies born to women who used marijuana during pregnancy are more likely to have a lower IQ, decreased spatial reasoning, learning and memory problems, be anemic, have lower birth weights, require placement in neonatal intensive care — and be more at risk for suicide and drug use later in life, according to the results of other recent studies.

Related: Straight Talk on Marijuana and Fertility

“This is what happens when state marijuana policies are a corporate free-for-all,” said Jeffrey Zinsmeister, executive vice president for Smart Approaches to Marijuana, based in Washington, D.C.

“Pot companies are touting marijuana as a modern-day snake oil, capable of curing almost anything under the sun, with zero [Food and Drug Administration] oversight. And they are now financing initiatives to allow pot ads on TV and marijuana smoking in restaurants. We’re regressing to 1960s-era smoking policies in the 21st century, just to make a few people rich. We know what the massive costs of those policies were with tobacco, especially on America’s children — and if the trend continues, we are going to do it all over again.”