Jan. 29, 2009 -- There is growing evidence linking very premature birth to a dramatic increase in autism risk, but more study is needed to confirm the association.
Last spring, researchers from Harvard Medical School and McGill University reported that one in four very low birth weight preemies showed early signs of autistic behavior when evaluated before age 2 in a study involving 91 children.
The studies don't prove that extreme prematurity is directly linked to autism because the children who participated were too young to have a confirmed diagnosis, lead author Ken C. K. Kuban, MD, of the Boston University School of Medicine tells WebMD.
"We should know more in a few years if we are able to follow these children," he says.
Early Birth and Autism
The study included close to 1,000 children born at least three months early between 2002 and 2004, enrolled in a larger trial.
When the children reached age 2, they were tested for early signs of autism spectrum disorder using a widely used screening tool known as the Modified Checklist for Autism in Toddlers (M-CHAT).
When the M-CHAT is used to screen children during routine pediatric visits, about 5% test positive, Kuban says.
By comparison, 21% of the very premature children in the study had positive M-CHAT scores.
Slightly more than one in four (26%) had birth-related health issues, including cerebral palsy (11%), visual impairments (3%), and hearing impairments (2%).
The risk of having a positive M-CHAT increased 23-fold among children unable to sit or stand by themselves, eightfold among children with visual and hearing impairments, and 13-fold among children with severe mental impairment.
Nearly half of the children with cerebral palsy and two-thirds of the children with visual or hearing problems tested positive on the M-CHAT screen.
"Children who had these impairments were more likely to be M-CHAT positive, but that didn't mean they were necessarily at higher risk for autism," Kuban says. "The message to pediatricians is that they need to be cautious in interpreting the results of this screening test in children with these handicaps."
Healthier Preemies Scored Better
When these children were excluded from the analysis, 10% of 2-year-olds without these disabilities still tested positive.
The study appears in the January issue of the Journal of Pediatrics.
"Children who had no motor, hearing, visual, or cognitive impairments still had double the risk of being M-CHAT positive," Kuban says.
March of Dimes Medical Director Alan Fleischman, MD, tells WebMD that it is clear that very premature children -- those born more than two months early, weighing 3 pounds or less -- are at high risk for a wide range of birth-related developmental problems.
But it is not clear that those problems include autism spectrum disorder, he says.
"If a baby's brain has been hurt by the consequences of extreme prematurity, it isn't surprising that they display these symptoms, but I'm not sure it is helpful to label it autism," he says. "Certainly, these babies need to be evaluated closely. That is an important message."