The likelihood of a school-aged American child receiving a diagnosis of autism, Asperger syndrome or a related developmental disorder increased 72 percent in 2011-12 from 2007, according to an analysis of a phone survey of parents released Wednesday by the Centers for Disease Control and Prevention and the Health Resources and Services Administration.

According to experts not involved in the report, the increase coincided with a period of soaring awareness of autism spectrum disorders among clinicians and schools, as well as parents.

The report emphasized that while the numbers changed from 1 in 86 children, ages 6 to 17, having received a diagnosis in a 2007 parent survey, to 1 in 50 children in the current report, most of the increase was because of previously undiagnosed cases.

“Our findings suggest that the increase in prevalence is due to improved recognition of autism spectrum disorders,” said Stephen J. Blumberg, a senior scientist with the centers’ National Center for Health Statistics and the lead author of the study, “as opposed to children with newly developed risks for them.”

Parents in the newer survey who reported that their children had received a diagnosis between 2008 and 2012 were far more likely to report that the diagnosis had been characterized as “mild” than parents who received the diagnosis earlier.

In keeping with earlier studies about autism spectrum disorders, the new report reflected gender disparities. In the new study, 1 in 31 boys had received a diagnosis, up from 1 in 56 boys in 2007. By contrast, 1 in 143 girls received a diagnosis, according to the latest report; in 2007, 1 in 204 girls received a diagnosis.