Link established between birthweight and autism

An analysis of Swedish health records by researchers at the University of Manchester has demonstrated that both very small and very large babies exhibit a greater risk of developing autism.

The group, led by Professor Kathryn Abel, analysed more than 40,000 health records in the biggest study of fetal growth and autism reported in the scientific literature. Figures were obtained from the Stockholm Youth Cohort, a huge databank comprising 589,114 children aged 0-17 who lived in Stockholm County between 2001 and 2007.

Autism is a lifelong developmental disability which manifests as restricted, repetitive and stereotypical forms of behaviour in addition to impaired communication and social interaction. It exists as a broad spectrum of disorders – including Asperger’s syndrome and “classic” autism – which produce disability to a variable extent. Both genetic and environmental factors are believed to contribute to the development of this incurable condition, recently estimated by the NHS to affect as many as 1/100 British children.

After excluding several groups (such as those too old to be diagnosed with autism, and children born outside Sweden), the researchers made comparisons between 4,283 children with autism and 36,588 age-matched controls. They found that babies weighing more than 9Ib 5 had a 60% greater risk of developing autism than babies with normal growth. Moreover, babies weighing less than 5.5lb at birth displayed a 63% increased risk of developing autism. In both cases, the effect was significant irrespective of pre-term and post-term birth.

The results have led Professor Abel to speculate that the high risk of autism in these groups reflects developmental abnormalities that may involve the placenta. She encourages further research into the control of fetal growth and the development of the human brain in order to elucidate the molecular and cellular mechanisms underlying the association between autism and extremes of fetal growth.