Low birthweight may increase autism risk

The prevalence of autism is higher among low birthweight or preterm children, particularly in females and in children with other developmental disabilities, according to research published in the June issue of Pediatrics.

Diana Schendel, PhD, and a colleague at the National Center on Birth Defects and Developmental Disabilities at the Centers for Disease Control and Prevention, conducted a two-part retrospective cohort study of 434,091 surviving children born in Atlanta between 1981 and 1993, and sorted out those with developmental disabilities as defined by the Metropolitan Atlanta Developmental Disabilities Surveillance Program. In the second step, they took a nested case-controlled sample from the cohort of 617 children identified as having autism and a control group of subjects who were not identified as having developmental disabilities.

The investigators found that birth at fewer than 33 weeks' gestation and birthweight under 2,500 g were associated with roughly twice the risk of developing autism, although the risk varied according to gender and autism subgroup (higher among girls and for those with autism accompanied by other developmental disabilities). Girls with a low birthweight were four times as likely to have autism accompanied by mental retardation, although boys with a low birthweight were not at greater risk for autism alone, the report indicates.

"Gender and autism subgroup differences in birthweight and gestational age, resulting in lower gender ratios with declining birthweight or gestational age across all autism subgroups, might be markers for etiologic heterogenicity in autism," the authors conclude.

Schendel D, Bhasin TK. Birth weight and gestational age characteristics of children with autism, including a comparison with other developmental disabilities. Pediatrics. 2008;121:1155-1164. doi:10.1542/peds.2007-1049.