Jan. 29, 2009 -- Among the many serious health risks faced by babies born extremely prematurely, an increased risk of autism may confront moms-to-be, a new study suggests.
Autism is characterized by difficulty with social interaction, problems with all forms of communication and repetitive behaviors or obsessive interests. Depending on where a patient falls on the autism spectrum, the severity of these behaviors can range from mild to disabling.
Using a special questionnaire, researchers from Boston University and Wake Forest University in Winston-Salem in North Carolina found that even among children with no pre-existing impairments, the chances of developing autism were about twice as high in those born three months early compared to children born within the normal range of gestation.
Lead study investigator Dr. Karl Kuban, chief of the Division of Pediatric Neurology at Boston Medical Center, cautioned that the test is not conclusive in determining whether a child will develop autism.
"You have to acknowledge that a positive screen isn't the equivalent of autism," Kuban warned.
In light of this, he added, his findings may also be seen as an indication that the questionnaire is far more prone to a false positive -- in essence, indicating that a child has autism when he or she does not -- than many might believe.
But what the test could do is give medical professionals a heads up when it comes to premature children, cluing them in that they might be at greater risk of being diagnosed with autism later on in life.
"It is increasingly clear that while we have made giant strides in supporting lungs, kidney and other immature organs to maturity, brain development does not do so well outside the womb," said Dr. Shlomo Shinnar, professor of neurology and pediatrics at Montefiore Medical Center in the Bronx, New York.
"Extreme prematurity is associated with an increased risk for a variety of cognitive and behavioral disturbances, so in retrospect we should not be shocked that this is also true for autism."
Linking Premature Birth and Autism Risk
In the study, the children's parents or care givers answered a questionnaire called the modified checklist for autism in toddlers (M-CHAT) when the toddlers were 2 years old. The M-CHAT checklist is a tool used to screen young children who are at risk for autism.
No Pre-Existing Conditions
The researchers found that 21 percent of all the premature toddlers who were screened tested positive on the M-CHAT test.
Investigator Kuban noted that children born at least three months prematurely commonly suffer from motor, hearing or vision impairments, thereby increasing their chances of testing positive on the M-CHAT screening. So, in order to glean a clearer picture of the risk for developing autism in children born extremely prematurely, the researchers took out the children with pre-existing impairments and screened the remaining children with the M-CHAT checklist.
Even after taking these children with pre-existing conditions out, Kuban and his team found that about 10 percent of the children tested positive for autism, nearly double the expected rate.
"If you get a high rate of M-CHAT positive screenings even after taking out cognitively impaired children, then I think it's an indication of something else," Kuban said.
Getting to the Roots of Autism
The Centers for Disease Control and Prevention (CDC) estimates that between two and six per 1,000 children have an autism spectrum disorder, or somewhere between one in 500 to one in 150. The risk is three to four times higher in males than females.
Autism is an extremely complex disorder, the causes of which are the subject of great debate among experts and laypeople alike. While many experts say that autism can be caused by genetic and environmental factors alike, it remains unclear which factor plays a bigger role in the onset of the disorder.
But these findings provide little additional information on the various mechanisms of the disorder. Rather, said Dr. Sessions Cole, director of the Division of Newborn Medicine at the Washington University School of Medicine in St. Louis, Mo., the study highlights the potential shortcomings of using the M-CHAT checklist to screen young children for autism.
An Early-Warning System
"This report is more about the high false positive values of autism screening tools like the M-CHAT in extremely preterm infants than it is about the causes of autism," he said. "I think providing parents with anticipatory guidance is always a good idea. The problem is that the tool used to provide such a warning should be reasonably accurate -- that is, have a high positive predictive value."
Still, others said the M-CHAT test provides doctors and parents alike with useful information about their child's cognitive function and development. And Dr. Nancy Minshew, professor of psychiatry and neurology at the University of Pittsburgh, said that the test's use as an "early warning" for a possible increase in autism risk could, indeed, be useful.
"Knowledge is helpful and leads to interventions to promote social communication and social contact," she said.