The last thing a parent wants to do is hurt their child, but unfortunately, alcohol consumption during pregnancy is a leading cause of children’s developmental disabilities worldwide. Now, a new study suggests the prevalence of fetal alcohol spectrum disorders among American children is greater than previously believed.

According to research published in the the Journal of the American Medical Association, fetal alcohol spectrum disorders may affect as many as one in 20 American children. That’s a huge jump from the previous estimate of one in 100.

Funded by the National Institute on Alcohol Abuse and Alcoholism (NIAAA), the study assessed nearly 3,000 first-graders at public and private schools in four American communities. The children were evaluated for cognitive and behavioral problems associated with Fetal Alcohol Spectrum Disorders, the umbrella term for a range of neurological and physical impacts caused by exposure to alcohol in the womb.

Researchers also interviewed mothers and close relatives to assess each child’s prenatal alcohol exposure.

The results of the study suggest children living with FASD are often undiagnosed. More than 200 of the first-graders experiencing learning and behavioral challenges fit the criteria for a diagnosis of FASD during the course of the study, but only two of the kids had previously received that diagnosis.

“Estimating the prevalence of FASD in the United States has been complex due to the challenges in identifying prenatally exposed children,” says George F. Koob, Ph.D, the Director of the the National Institute on Alcohol Abuse and Alcoholism, which funded the research.

“The findings of this study confirm that FASD is a significant public health problem, and strategies to expand screening, diagnosis, prevention, and treatment are needed to address it,” Koob says.

While some controversial studies have suggested light drinking during pregnancy may not be harmful and that red wine may help women conceive quicker, the American Academy of Pediatrics says no amount of alcohol should be considered safe.

According to the Centers for Disease Control, one in 10 pregnant women reports drinking alcohol despite the CDC warning against it. The CDC recommends even women who are not yet pregnant but are trying to conceive don’t drink any alcohol at all.

As the New York Times notes, experts say that while some evidence suggests the more a mom drinks, the greater the damage will be, in some women even a small amount of alcohol isn’t safe. Because every mother—and every fetus—is impacted by alcohol differently, it’s impossible to determine a safe amount.

The threshold at which a dose of alcohol impacts a fetus depends on individual metabolism, genetics and gestational age, meaning that in some cases, a small amount of alcohol may result in a child being born on the fetal alcohol spectrum.

There is some push-back to the study, with the authors even acknowledging the results seen in the four selected communities may not be representative of the country as a whole. Critics of the study say further research is needed to more accurately estimate the prevalence of FASD among American children.

Nonetheless, the authors of the JAMA study hope their work underscores the message that women should cease all alcohol consumption during pregnancy. It also suggests there should be more programs to help expectant mothers who struggle with drinking, and tools for parents of children who struggle with FASD.