Why Autism Diagnoses Have Soared

The number of children diagnosed with autism spectrum disorder (ASD) has risen consistently and dramatically since the 1990s. Researchers have been working to determine why and when autism started to rise.

There's no single reason for this increase, but several changes are likely behind the shift.

This article will discuss the main theories about why autism is rising, including increased awareness, changes in reporting practices, and environmental factors like parents' age and maternal health.

autistic girl playing

timnewman / Getty Images

According to the Centers for Disease Control and Prevention (CDC), as of 2020, approximately 1 in 36 children age 8 in the United States was diagnosed with autism. In 2000, the corresponding rate was approximately 1 in 150 children.

Evolving Diagnostic Criteria

Autism was first described during the 1940s and included only those children who displayed intense autism traits. These traits might be described today as "level 3" autism spectrum disorder, with high support needs.

In 1994, the American Psychiatric Association released the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), which recognized autism as a spectrum disorder. In essence, it became possible for someone to display mild autistic traits or more profound autistic traits.

New diagnoses, including Asperger's syndrome and the catch-all Pervasive Developmental Disorder Not Otherwise Specified PDD-NOS, were added to the manual. Neither of these terms are used today.

Upon publication of the most recent version of the manual (DSM-5) in 2013, Asperger's and the other diagnoses were eliminated and folded into a single diagnosis of Autism Spectrum Disorder, or ASD. This may mean that more people fit the criteria for an autism diagnosis, resulting in a rise in reported cases.

Screening Guidelines for Autism

Continued awareness of autism has resulted in increased routine screening by pediatricians, another contributing factor to a rise in cases. The American Academy of Pediatricians recommends that all children be screened for ASD at ages 18 months and 24 months, along with regular developmental surveillance.

Changes in Reporting Practices

The CDC's report on autism statistics is based on health and school records for 8-year-old children who live in select counties across the United States. The researchers are part of the Autism and Developmental Disabilities Monitoring Network, which the CDC set up in 2000 to estimate autism prevalence.

Clinicians scanned the school records for children with signs of autism traits, such as social problems or repetitive behaviors. They use data from 8-year-olds because most children are enrolled in school and have had routine health assessments by that age. However, the data is not based on whether children have been diagnosed with ASD.

Up until 1990, autism was not included in legislation aimed at guaranteeing an education to individuals with disabilities. In 1990, the Individuals with Disabilities Education Act added autism to its list of conditions covered under the act. The new law also added transition services and assistive technologies to its requirements. Autism had never been tracked as an educational statistic before 1990. Since 1990, the incidence of autism in schools has risen dramatically.

Another set of prevalence estimates published in Pediatrics in 2019 found that autism in the United States rose from 1 in 91 children in 2009 to 1 in 40 in 2017. The results were based on telephone or in-person interviews with the parents of 88,530 children aged 3 to 17, collected by the CDC as part of its National Health Interview Survey.

Experts attribute the rise to growing awareness of ASD and improved systems for identifying autistic traits in children. It is important to note that racial and ethnic minorities, as well as all children from a lower-income background, are typically less likely to receive a diagnosis of autism. However, experts believe there is not an actual difference in the number of children from these backgrounds affected. Increased health equity measures will help to close the gap in diagnosis and early intervention for all kids with ASD.

Possible External Factors

The cause of autism is unknown, though research has pointed to a combination of genetic and environmental factors. For example, a child is at greater risk if they have an autistic sibling.

Other evidence involves certain environmental factors occurring before or during birth. These include:

  • Advanced parental age
  • Prenatal exposure to air pollution or certain pesticides
  • Maternal obesity, diabetes, or immune system disorders
  • Extreme prematurity or very low birth weight
  • Any birth difficulty leading to periods of oxygen deprivation to the baby's brain

Some of these factors may be increasing, which could theoretically lead to increasing rates of autism. For example, roughly 20% of women in the United States have their first baby after age 35.

There have been many other incorrect theories about environmental causes of autism, including vaccines, poor nutrition, "bad" parenting, and cell phone use, among others. All of these have been debunked.

Will Diagnoses of Autism Continue to Increase?

There is no way to know if autism rates will continue to rise. As diagnostic criteria evolve, it could lead to more or fewer children being qualified for an autism diagnosis.

Shifts in environmental factors that may contribute to autism can also impact whether the prevalence of autism grows. For example, if people wait until they are older to have children, autism and other conditions related to advanced parental age might rise.

Some experts expected a decline in autism diagnoses once Asperger's syndrome and PDD-NOS were eliminated as catch-all options. Others expected an increase as awareness and services improve. For now, the number and rate of children diagnosed with autism continue to rise.

Summary

Since the 1990s, the number of documented cases of autism has risen dramatically. Factors like diagnostic criteria, how cases of autism are reported, and increased awareness are all contributors to this increase. Reporting now-outmoded conditions like Asperger's and PDD-NOS under the umbrella of autism spectrum disorder also skewed the statistics. Cases are expected to continue to rise for now.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Lisa Jo Rudy
Lisa Jo Rudy, MDiv, is a writer, advocate, author, and consultant specializing in the field of autism.