April 2, 2008 -- Very premature birth may be a major risk factor for autism, but more study is needed to confirm the association, researchers say.
One out of four very-low-birth-weight babies -- weighing as little as 1 pound at birth and no more than 3.3 pounds -- showed signs of autistic behavior when screened as toddlers in a study published in the April issue of the journal Pediatrics.
The children, who are now preschool age, are undergoing further testing to determine if they meet the diagnostic criteria for autism or related disorders.
"The very-low-birth-weight babies in our study did show a high prevalence of autistic behaviors in early screening," study researcher Catherine Limperopoulos, PhD, tells WebMD. "The next step is to determine if what we are seeing in these early screenings really is autism."
Premature Birth and Autism
Ninety-one very-low-birth-weight children were included in the study, conducted by researchers from McGill University and Harvard Medical School.
All were less than 3.3 pounds at birth, with gestational ages of 23 weeks to 30 weeks.
In addition to routine developmental testing, the children were evaluated for signs of autism between the ages of 18 months and 24 months, using accepted early screening tests.
Twenty-three of the 91 children (25%) had abnormal results on a screening tool for behaviors associated with autism.
Boys were six times as likely as girls to have an abnormal score on the screening test, and lower gestational age and weight at birth were also associated with abnormal scores.
"The smallest and sickest babies seemed to be most at risk," Limperopoulos says.
The biggest single risk factor for a positive test was inflammation, usually from a bacterial infection occurring before or during labor known as chorioamnionitis.
The condition was associated with a 16-fold increase in very-low-birth-weight babies testing positive for symptoms related to autism.
Early Autism Screening Needed
Though the findings do not prove a link between very low birth weight and autism, they do suggest a need for early screening in babies born weighing less than 3.5 pounds, Limperopoulos says.
"We routinely screen these babies for language delays and motor difficulties," she says. "Early autism screening should also be routine."