Fact check: Has autism prevalence increased?

President Donald Trump said Feb. 14 there's been a "tremendous" increase in autism in U.S. children. Is this true?

There has been a "tremendous" increase in the number of reported cases of autism since the 1990s, according to FactCheck.org. The Center for Disease Control reports autism cases increased from 3.4 per 1,000 in 1996 to 14.6 per 1,000 in 2012.

But what's unclear is if more children have autism, or if more children are being diagnosed with autism. It's a key difference, according to FactCheck.org. 

Trump suggested more children are suffering from autism, but researchers suggest the increase is due to greater awareness of autism spectrum disorder and its wide range of symptoms. The definition of ASD has broadened over the years, and doctors may be reclassifying children with "intellectual disability disorder" as ASD. Also, researchers aren't finding an increase in special education enrollment, suggesting the increase in ASD is more reclassification than increase in the actual number. 

Research continues on the causes of ASD, leaving the possibility of an increase in actual cases. FactCheck.org notes a mother's age can be a risk factor for autism, and women, on average, are having babies at later ages.

Undoubtedly true is the increase in reported cases of autism over the past two decades. Less clear is whether the increase is better or different diagnoses, or an actual increase in the prevalence of autism. 

Read FactCheck.org's detailed fact check here, including citations to research and a nuanced discussion of the issue, including a graph showing the decline of "intellectual disability" diagnoses in step with the increase in "autism" diagnoses.