As many as 5 percent of children may have some type of fetal alcohol spectrum disorder (FASD), caused by alcohol exposure before birth, a new study suggests.

Researchers at the University of North Carolina, Chapel Hill, found between 2.4 percent and 4.8 percent of children have FASD, HealthDay reports. “Knowing not to drink during pregnancy and not doing so are two different things,” particularly before a woman finds out she is pregnant, said lead researcher Philip May.

The study appears in the journal Pediatrics.

According to the National Organization on Fetal Alcohol Syndrome, FASD is an umbrella term describing the range of effects that can occur in a person whose mother drank alcohol during pregnancy. These effects may include physical, mental, behavioral, and/or learning disabilities with possible lifelong implications.

Fetal alcohol syndrome is the most severe type of FASD. It is characterized by growth retardation, structural brain abnormalities and specific facial characteristics. The researchers note children on the less severe end of the spectrum may have behavioral issues or difficulty completing tasks required to do well in school.

To estimate the prevalence of FASD, the researchers looked at data from a nationally representative town in the Midwest. The researchers identified first graders who had a developmental problem or who were below the 25th percentile for height, weight or head circumference. These children were given behavior and memory tests, and their results were compared with those of a group of typically developing peers. Children were also assessed for physical signs of FASD.

The researchers concluded between six and nine of every 1,000 children had fetal alcohol syndrome and between 11 and 17 per 1,000 children had partial fetal alcohol syndrome. These estimates are higher than those found in previous research, the article notes.