Babies born small or prematurely go on to develop autism at higher rates, although the risk is still small, according to a new study from Finland.

The research is part of a global push to identify the culprits behind the developmental disorder and the recent uptick in its occurrence.

"Previous reports of how .or gestational age is associated with autism have not been consistent," Dr Andre Sourander, a psychiatrist at Turku University, said.

"Because autism spectrum disorders are one of the major challenges in child mental health it is extremely important to get more understanding of its causes," Dr Sourander said.

The new results, published in The Journal of Pediatrics, are based on almost two decades' worth of data from more than one million births in Finland.

Smoking ups  risk of autism

As of 2005, the rate of autism in the Northern European country was nine per 10 000 children in Finland, whereas Asperger syndrome was diagnosed in 14.5 children out of 10 000.

After accounting for the mother's age, smoking, number of previous births, and other factors, Dr Sourander's team found an increased risk of autism, but not Asperger syndrome, in preemies and babies that were very small at birth.

For instance, those who weighed less than 1 000 g at birth had three times the odds of developing autism.

(Reuters Health, Frederik Joelving, July 2012)

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