For the first time in over a decade the federal government is releasing new data on the number of children with developmental disabilities, reporting that diagnoses have grown significantly since the 1990s.

About 1 in 6 U.S. children are diagnosed with a developmental disability, according to a new Centers for Disease Control and Prevention study published online in the journal Pediatrics Monday. That represents an increase of 17 percent between 1997 and 2008 alone.

The rise was largely due to growth in cases of autism, attention deficit hyperactivity disorder and the catch-all category of “other developmental delays,” according to Coleen Boyle, director of the National Center on Birth Defects and Developmental Disabilities at the CDC, who led the study.

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While it’s not exactly clear why the number of children with developmental disabilities is increasing, researchers said factors such as parents having kids later in life, more premature births and the use of fertility treatments could be contributing.

For the study, which relied on data collected over an 11-year period, parents of nearly 120,000 kids ages 3 to 17 were asked in in-person interviews if their child had a diagnosis of intellectual disability, cerebral palsy, autism, ADHD, seizures, stuttering, hearing loss, blindness, learning disorders or other developmental delays.

If anything, the new statistics may be an underestimate, says Gary Goldstein, president and CEO of the Kennedy Krieger Institute, a leading research and clinical center focused on developmental disabilities.

While Goldstein believes the study methodology used in the CDC effort is valid, he says underreporting is common in parent surveys since inevitably some parents may not be forthcoming about a disability or may not know their child qualifies for a diagnosis.

“If you went and examined all of these children, I think you’d find a higher number than this,” Goldstein says.