The U.S. government increased its autism estimate on Thursday to 1 in 68 children, a 30 per cent jump from the last estimate of 1 in 88 children.

Those numbers include children with autism or a related disorder, and they correspond with data in the most recent Canadian study.

A report from the National Epidemiologic Database for the Study of Autism in Canada released in 2012 found increases in autism diagnoses in Prince Edward Island, Newfoundland and Labrador and southeastern Ontario. The increases ranged from 39 to 204 per cent, depending on the region and age group.

The latest calculation from the U.S. Centers for Disease Control means autism is more than twice as common as officials said it was just seven years go.

The CDC report estimates that 1.2 million children or teens are affected by the disorder.

Much of the increase is believed to be due to increased awareness of the disorders, and suggests doctors are diagnosing autism more frequently, especially in children with milder problems.

Because there are no blood or neurological tests for autism, doctors base their diagnosis on a child’s behaviour. Four of the main criteria are:

  • trouble communicating
  • problems with social interaction
  • repetitive behaviours
  • unusual, or severely limited interests

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“I don’t want people the panic,” Dr. Evdokia Anagnostou, a child neurologist and autism researcher at Holland Bloorview in Toronto, told CTV News. “Yes, the trend is upwards, but it may be the result of better diagnosis.”

She said higher rates in urban centres could be due to more services for children with ASD.

In earlier decades, an autism diagnosis was confined to children with severe language, intellectual and social impairments and unusual, repetitious behaviours. But the definition has gradually expanded and now includes milder and related conditions that cause social and learning problems for children.

There’s a clue in the U.S. data, showing that 46 per cent of the children now diagnosed with Autism Spectrum Disorder have average to above average IQ, suggesting that the diagnosis is being made in more high-functioning children. In earlier studies, autism was thought to affect mainly children with severe intellectual disabilities.

In the recent Canadian and U.S. studies, there was troubling news that children from lower economic groups and regions have lower rates of diagnosis -- likely because fewer services to spot and treat autism are available.

The Canadian study, for example, showed about 1 in 100 children are diagnosed with ASD, but doctors think it’s not because fewer children have the disorder than in the U.S.

“It would suggest that more work needs to be put into areas where diagnosis is low. It suggests if we don’t have the services we won’t make the diagnosis,” Dr. Anagnostou said. “If we don’t have the accurate numbers, we can’t develop the services.”

Both the U.S and Canadian research also noted that the average age of diagnosis of ASD is about 4.5 years of age even though there are reliable tests to make the call by age 2.

Experts say earlier diagnoses means more intensive therapy can begin sooner, possibly lessening the symptoms of Autism Spectrum Disorders.

The data confirmed that boys are far more likely to be diagnosed, with one in 42 – developing some form of autism, compared to 1 in 189 girls.

Scientists say they don’t understand why, but are conducting research on genetic factors and possible environmental triggers. Another study released Thursday points to in-utero development of the disorder.