A new study suggests that low birth weight could be among the potential environmental risk factors for autism spectrum disorder.

The study of 3,715 same-sex twin pairs participating in the Child and Adolescent Twin Study of Sweden (CATSS) was published in the journal Psychological Medicine.

The study obtained parents’ birth weight records by the Swedish Medical Birth Registry and found that twins lower in birth weight in (autism spectrum disorder-discordant (ASD) twin pairs were more than three times more likely to meet criteria for ASD than heavier twins.

“Analysis of the effect of birth weight on ASD symptoms in the entire population, most of whom did not have ASD, showed a modest association,” the authors said.

They found that for every 100 gram increase in birth weight there was a 2 percent decrease in severity of ASD.

The authors concluded that although genetic effects are important factors in autism, “a non-genetic influence associated with birth weight may contribute to the development of Autism.”