The cohort contained records of 589,114 children aged 0-17 in Sweden between 2001 and 2007. Certain child data was removed, including children too young to have a diagnosis for ASD, adopted children and non Swedish or Stockholm County residents, children not born in Sweden and twins.
From the remaining available data, researchers found 4,283 young people with autism and 36,588 who did not have the condition and who acted as the control.
The study found that bigger babies who were born weighing over 4.5kg (or 9lb 14) showed a higher incidence of autism, as did smaller infants who were born weighing less than 2.5kg (5.5lb).
A baby who had poor fetal growth would therefore have a 63% greater risk of developing autism compared to normally grown babies.
A baby who was large at birth would have a 60% greater risk. This effect was independent of whether or not the baby was born pre or post term.
Professor Abel added: "We think that this increase in risk associated with extreme abnormal growth of the fetus shows that something is going wrong during development, possibly with the function of the placenta.
"Anything which encourages abnormalities of development and growth is likely to also affect development of the baby's brain. Risk appeared particularly high in those babies where they were growing poorly and continued in utero until after 40 weeks. This may be because these infants were exposed the longest to unhealthy conditions within the mother's womb.
"We now need more research into fetal growth, how it is controlled by the placenta and how this affects how the brain develops. One of the key areas to research is maternal condition and healthy growth."
The study was also unique as it was big enough to be able to look at the differences between children who developed ASD with and those without intellectual disability as well as differences between children born pre and post-term (after 40 weeks).
|Contact: Alison Barbuti|
University of Manchester