That number appears to be on the rise. In 1997-1999, about 12.8 percent of kids were diagnosed with a developmental disability. That number rose to 15 percent in 2006-2008 -- or an additional 1.8 million U.S. children.
Much of the bump up in cases seems driven by rising rates of autism and ADHD, experts say.
"The most important message here is raising awareness of the importance of this as a health problem and one we need to address," said lead study author Coleen Boyle, director of the U.S. National Center on Birth Defects and Developmental Disabilities. "Children are our future, and many of these children can grow up to be very productive citizens, so we need to invest in programs to help facilitate their development."
Researchers used data from the 1997-2008 National Health Interview Surveys, an annual, nationally representative survey of U.S. households. The surveys asked parents of children aged 3 to 17 if their children had been diagnosed with ADHD, intellectual disability, cerebral palsy, autism, seizures, stuttering or stammering, moderate to profound hearing loss, blindness, learning disorders and/or other developmental delays.
Nearly 10 million U.S. children had been diagnosed with one of those conditions in 2006-2008, according to parental reports.
Much of the increase is being driven by ADHD and autism diagnoses, Boyle said. About 7.6 percent of children were diagnosed with ADHD in 2006-2008, up from 5.7 percent in 1997-1999. About 0.74 percent of kids had received in autism diagnosis in 2006-2008, up from 0.19 percent in 1997-1999.
The number of children slotted under "other developmental delays," a catch-all category, also rose from 3.4 percent to 4.24 percent.
The study is published online May 23 and in the June print issue of Pediatrics.
So, are the number of children with developmental disabilities on the rise, or are parents and doctors getting better at detecting cases? According to Dr. Nancy Murphy, chair of the American Academy of Pediatrics' Council on Children with Disabilities, the increases in these conditions may signify a greater awareness on the part of parents, teachers and health care professionals to identify children with disabilities and get them help.
That could mean that kids that might have been dismissed as simply being "slow" or disobedient in the past may now be getting some extra help to realize their potential, Murphy said.
"It speaks to providers and educators and parents being attentive to when kids are struggling, and that attentiveness is bringing them into systems that can generate diagnoses," Murphy said. "There is a greater willingness to say, 'My kid is struggling -- not because he's a bad kid but he may need a different approach to learning or development or behavior than he or she is getting.'"
One unanswered question is whether greater awareness and efforts to diagnose kids is the only explanation, or if there actually are a greater percentage of kids who are being born with or developing disabilities such as autism and ADHD early in life.
Research has suggested that advanced maternal and paternal age, assisted reproductive technology and greater numbers of premature or late-preterm births, could all be factors in some developmental disabilities, Boyle said. However, those are areas that need much more research, she added.
Improvements in medical technology also means that children born with very serious developmental disabilities, such as neuromuscular or chromosomal disorders, are now surviving conditions that would have killed them in the past. That could also explain some of the uptick in numbers, Murphy said.
In other findings, boys were more likely to have a developmental disability than girls. Hispanic children were the least likely to be diagnosed with a number of disabilities, compared with white and black children.
Children with public insurance, mainly Medicaid, were more likely to have disabilities than those on private insurance plans.
And although rates of autism and ADHD were up, other developmental conditions remained basically steady, including blindness and intellectual disability, while moderate to profound hearing loss showed a significant decline.