The number of children with developmental disorders, including autism and attention deficit hyperactive disorder, has increased by 17 percent between 1997 and 2008 in the United States, according to a new study.

That means that in 2008, 15 percent of all U.S. children or nearly 10 million children had a developmental disorder, according to the study.

However, the numbers are likely a combination of increased reporting and decreased stigmatization of the disorders, as well as higher parental ages that put kids at an increased risk for these disorders, said study researcher Laura A. Schieve, an epidemiologist at the National Center for Birth Defects and Developmental Disabilities at the Centers for Disease Control and Prevention.

The study was published today (May 23) in the journal Pediatrics.

ADHD and autism increases

The results of the study are based on a nationally representative sample of children ages 3 to 17. Their parents reported whether the children had attention deficit hyperactivity disorder , autism, cerebral palsy, seizures, stuttering, intellectual disability, stammering, hearing loss, blindness, learning disorders or developmental delays.

Researchers found an increase in developmental disorders such as autism and attention deficit hyperactive disorder . Autism had the greatest increase over the study period, increasing from 0.19 percent of children at the start of the study to 0.74 percent of children at the end of the study.

Attention deficit hyperactive disorder increased from 5.7 percent to 7.6 percent over the study period, according to the data.

Researchers also found a decrease in moderate to profound hearing loss. However, this is the first study to show a decrease in hearing loss, so "we consider this an early finding that needs to be assessed again in the future to better understand whether there is a long-term trend," Schieve told MyHealthNewsDaily.

Reporting and risk factors

While it's possible that more kids today have these disorders than in 1997, an increase in the reporting and diagnosis of the developmental disorders likely plays as big role, Schieve said.

"There has been an increased emphasis on early treatment and interventions for children with developmental disorders and a likely corresponding increase in the availability of both treatment and diagnostic services," she said.

And improvements through the years in clinical, parental, and societal recognition of and screening for these disorders could also have boosted the reporting rate, she added.

But while increases in reporting are likely a big factor in the study results, it's important to consider that these trends may be related to changes in prenatal risk factors for these conditions, Schieve said. For example, shifts toward later parental ages in the United States have been associated in past studies with adverse developmental outcomes in children .

Pass it on: Developmental disorders, including autism and attention deficit hyperactive disorder, have increased by 17 percent in the U.S. over the last 12 or so years.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.