Low Birth Weight May Be Risk Factor for Autism

In ASD-discordant twin pairs, lower birth weight tied to triple the risk of meeting ASD criteria

THURSDAY, Jan. 26 (HealthDay News) -- Low birth weight may be among potential environmental risk factors for autism spectrum disorder (ASD), according to a study of same-sex twins published online Dec. 2 in Psychological Medicine.

Molly Losh, Ph.D., of Northwestern University in Evanston, Ill., and colleagues analyzed the birth weights and screenings for ASD and other development disorders in a population-based cohort of 3,715 same-sex twin pairs from the Child and Adolescent Twin Study of Sweden. A structured parent interview was used to assess ASD and related disorders, and birth weights were collected from medical birth records.

The researchers found that, in the 34 ASD-discordant twin pairs, twins lower in birth weight had an increased likelihood of meeting criteria for ASD than twins with a higher birth weight (odds ratio, 3.25). Based on analyses of birth weight as a continuous risk factor, for every 100 g increase in birth weight, there was a 13 percent reduction in the risk of ASD. In the entire population, the effect of birth weight on ASD symptoms was modest. For every 100 g increase in birth weight, there was a 2 percent decrease in the severity of ASD, as measured by scores on the Autism-Tics, attention-deficit hyperactivity disorder, and other comorbidities inventory.

"The data were consistent with the hypothesis that low birth weight confers risk to ASD," the authors write. "Thus, although genetic effects are of major importance, a non-genetic influence associated with birth weight may contribute to the development of ASD."

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