The growing and powerful marijuana industry wants the public to believe that the drug they promote is harmless, or even beneficial for many medical conditions. But a major study of nearly 300,000 pregnant women in JAMA – the Journal of the American Medical Association – shows that getting high is dangerous for expectant mothers.

An appalling 19% of pregnant California women between 18 and 24 used pot regularly during the first months of pregnancy; among mothers under 18, a full 22% indulged.

Despite the belief that weed might help combat morning sickness discomfort, the CDC—the Center for Disease Control and Prevention—shows major perils for the unborn baby, including increased risk of low birth weight and serious developmental problems. Most women know they should avoid alcohol while bearing and then nursing a baby, but medical research shows they haven’t gotten the same important message about marijuana—which, despite its trendy popularity, threatens serious impact on both adults and their offspring.