Here's an advice for young couples -- make sure you don't delay your progeny too much, for a study says that babies born with either parent over the age of 35 are a higher risk of suffering from autism.

A team of researchers from Britain and Denmark has found that older parents increase the risk of autism in children -- in fact, the risk is up to 27 per cent higher than for those with younger parents.

Initially it was thought that the mother's age was more important in affecting whether a child developed autism. But, now, the researchers claim that the risk posed by the mother's and father's age are virtually the same.

They also found that if both parents are in their late 30s, the child's risk of having autism is no higher than if only one of them is, the 'Daily Mail' reported.

However, if one parent is under 35 and the other 40 or over, the extra risk of autism is greater with an older mother (65 per cent) compared with an older father (44 per cent), the study has revealed.

The researchers from University of Aarhus in Denmark and Cambridge University came to the conclusion after analysing 1.3 million children born in Denmark between 1980 and 2003.

Of those, 9,556 were later diagnosed with a disorder on the autistic spectrum by a child psychiatrist after being referred for treatment. This includes autism, Asperger's syndrome and other developmental conditions.

Professor Erik Thorlund Parne of Denmark, who led the study, said: "The (old) explanation was that new mutations in the sperm increase the risk for autism, and that new mutations in the egg increase the risk for autism.

One would then expect that if a couple had these particular mutations in both the sperm and the egg, then they would have a higher risk for autism than if only one parent had the particular mutation. We don't see this pattern."

Experts are not fully satisfied with the findings published in the 'Annals Of Epidemiology' journal.

Caroline Hattersley of The National Autistic Society said: "While this research suggests that there is a link between parental age and autism, more studies are needed to understand the factors."