A new study has found children with autism are more likely to have severe social symptoms if their mothers had chronic asthma or allergies while pregnant.

Key points: Researchers said the asthma and allergy link was only one of many possible biological pathways that could lead to autism in children

Researchers said the asthma and allergy link was only one of many possible biological pathways that could lead to autism in children Early diagnosis continued to be very important for kids with autism

Early diagnosis continued to be very important for kids with autism The research could lead to better healthcare options for families when they go to GPs

The research, published in the Molecular Psychiatry journal, involved testing 220 autistic children and examining the medical history of their mothers.

"We were looking for things like asthma, allergies, fevers, those sorts of things — as well as autoimmune conditions," said Professor Adam Guastella, from the Brain and Mind Centre at Sydney University.

"What we found were the children with mothers who had [those conditions] in pregnancy, those children showed greater severity of autism symptoms later in life."

No single cause of autism known

Professor Adam Guastella using toys to test the social responses of children. ( ABC News: Jade Macmillan )

The study was carried out in conjunction with Perth's Telethon Kids Institute, which stressed there was no single-known cause of autism.

"The absolutely wrong thing to take away from this study is that this is related to something a mother or a father has done during pregnancy," the institute's professor Andrew Whitehouse said.

"There are many, perhaps dozens, perhaps hundreds of different biological pathways through which a child can develop autism.

"What this study provides us is an inkling of one potential pathway and that's still a really important finding."

Professor Guastella said the study could lead to improvements in the way autism is diagnosed and treated.

"We know that early diagnosis is critical in terms of providing the best opportunities for young children," he said.

"We hope this will help us to provide more effective treatments so that when their families go to the GP they've got some adequate options."

'As a parent you do feel quite a bit of guilt'

Sydney mother Natalie Pollard knows the importance of early diagnosis.

Her autistic son Ethan was just a baby when she first started to worry about his behaviour.

"He'd been saying a few words, he'd started crawling and then almost overnight it just stopped," she said.

"There was no talking, there was no interacting, he would just sit in a corner and scream."

Seven-year-old Ethan Pollard playing in his Sydney home. ( ABC News: Jade Macmillan )

Ms Pollard said while she didn't suffer from asthma or allergies while she was pregnant, she welcomed any research which might improve understanding of autism and its causes.

"As a parent you do feel quite a bit of guilt and you often wonder why, is there something I could have done differently when I was pregnant or when Ethan was little?"

"Our main hope is that we can have him grow up and be happy and be able to function and integrate into the world. And to have a level of independence that at the moment we're not sure if he's going to have."