Belinda Hitchcock knew instinctively something was different with her baby.
Her placid son Bradley, who started talking when he was 18 months old, had regressed to incoherent babbling. By the time Bradley was two he had lost the ability to speak.
His mother was fobbed off again and again by doctors as she desperately tried to find answers.
"I thought, 'This is just not right. But everyone just kept saying, 'Don't worry he's a boy. He'll be fine'," Ms Hitchcock said.
More than a year after first seeking help, Ms Hitchcock paid $1000 to have her three-and-a-half-year-old son assessed privately.
"We went in, they checked him, they gave us the paperwork and said, 'He's autistic'," Ms Hitchcock said.
"Almost every day I think about that 12 months wasted and how much better he might be if we got him help earlier. Knowing that there was something wrong with my child and I couldn't help thinking I was horrible as a mother."
An estimated one in 100 children have Autism Spectrum Disorder, international studies suggest.
Early intervention from roughly 18 months offers the the best chance for improving outcomes, but the average Australian child with ASD is diagnosed at four years old, found a recent analysis of national data.
Belinda Hitchcock desperately searched for answers for 12 months before her son Bradley was diagnosed with autism.
Belinda Hitchcock desperately searched for answers for 12 months before her son Bradley was diagnosed with autism. Photo: Supplied
UNSW psychiatrist and researcher Professor Valsamma Eapen wants all children to be routinely screened for autism from six months to four years old.
"Fours years is really too late for a diagnosis. It's a huge missed opportunity," said Professor Eapen, who pushed for universal surveillance and early identification of ASD in a paper published in the Australian and New Zealand Journal of Psychiatry on Friday.
"The earlier the intervention the more gains the child makes in improving symptoms, and functional capacity. It's in those preschool years when brain plasticity is maximum that we can make those neuronal connections around speech and language and social connectedness," she said.
Professor Eapen suggested autism screening should piggyback the routine medical checks recommended for all children. NSW guidelines include nine checks between between six months and four years old including vaccinations and developmental markers.
Professor Eapen is calling for autism screening to be embedded within an overall developmental surveillance framework starting from six months and autism specific assessments from 18 months
"It's not about labelling these kids. An unresponsive child could have language or hearing problems, or autism. It's about finding kids who are falling behind and starting early intervention," she said.
Autism Awareness Australia chief executive Nicole Rogerson said delayed diagnoses were "absolutely devastating" for children.
"People say ridiculous things like, 'We'll just wait and see if it all just kicks in'. It's never going to just kick in for kids with autism," Ms Rogerson said.
"Parents are already freaking out if their children aren't hitting those developmental milestones. They're already anxious," she added, dismissing fears that a false positive diagnosis may cause unnecessary anxiety.
Identifying and treating ASD early may also ease the burden on services and public funding through NDIS as children are likely to improve faster and need less support for a shorter period of time, Ms Rogerson said.
Now nine-and-a-half, Bradley still does 20-30 hours of early intervention therapy each week. It took more than five years for his speech to return.
"I explain to people that it's like all the doors in his brain are shut and we are going through and opening each one individually as we go," Ms Hitchcock said.
"His behaviours are quite good now because he can tell us what he wants and his frustrations."
"But he has no social understanding at all. He doesn't have friends. He only just started playing with his sister Holly."
Ms Hitchcock said she has only recently started imaging Bradley's future.
"He'll probably never move out of home. He'll be with me and my husband forever.
"But I want him to be happy, and he is. I'm so proud of him. We would do anything for him. He enjoy seeing him improve and enjoy his achievements. He's phenomenal."
Autism and related disorders are the most common disability across trial sites for the NDIS, comprising about one-third of support packages. The $22 billion dollar scheme will roll out nationally from July this year.
NSW state funding for the NDIS will rise to more than $2 billion in 2016/2017, including $1.3 billion from the NSW Government and $740 million from the Commonwealth.
A panel of experts commissioned to advise the National Disability Insurance Agency recommended that children with ASD receive at least 20 hours a week in early intervention, which can cost up to $80,000 a year.
While the NDIA has not put a dollar figure on the cost of early intervention for ASD, it has previously estimated the price at between $16,000 and $18,000 a year.
Chief executive of the NDIA, David Bowen, said some children will need minimal assistance while others will need significant intervention and their packages will reflect their needs.