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."
She adds that it isn't yet clear if the behaviors associated with autism identified through screening are lasting or transient.
"This may be an early warning of autism spectrum disorder, but we just can't say yet," she says.
Case Western Reserve University researcher Maureen Hack, MD, has devoted much of her career to studying outcomes among premature and very-low-birth-weight babies.
She tells WebMD that it has long been clear that very premature babies have an increased risk for retardation and poorer neurodevelopment.
"The risk of brain injury related to extreme prematurity is very high," she says. "My bias is that this is nothing new. What they are calling autism may just be low cognitive development."
She adds that some earlier studies have identified cognitive and behavioral problems in as many as half of children born at very low birth weights.
"These children should definitely be tested very early for cognitive development, but I'm not sure that screening for autism adds anything," she says.