Researchers have uncovered fresh evidence that low birth weight increases the chance of a child developing autistic spectrum disorder (ASD) later in life.

However the latest study claims environmental factors play a key role too.

Researchers from Northwestern University looked closely at the findings from previous studies that investigated the ASD connection in identical twins. Earlier research suggests that when one identical twin has ASD, the other is much more likely to have ASD too, than not.

“This is because identical twins share virtually 100% of their genes,” explains researcher Molly Losh from the study.

However, the recent study argues that, “It is not 100% the case that ASD affect both identical twins in a twin pair” and that environmental factors need to be considered. It also found that lower birth weight more than triples the risk of ASD in identical twin pairs in which one twin had ASD and the other did not.

“Our study of discordant twins - twin pairs in which only one twin was affected by autism spectrum disorder - found birth weight to be a very strong predictor of autism spectrum disorder," says Losh.

"That only one twin is affected by ASD in some identical twin pairs suggests that environmental factors may play a role either independently or in interaction with autism risk genes," she added.

"And because autism is a developmental disorder impacting brain development early on, it suggests that prenatal and perinatal environmental factors may be of particular importance," adds Losh.

A previous study in October 2011 also highlighted the link between birth weight and autism.