NEW YORK - The risk of developing autism among children who were born prematurely is five times greater than among kids born after a full-term pregnancy, according to a new study.
"Although this group is not the first to report a higher prevalence of autism in the low birth weight infant population, they've done a better job than anyone else in confirming the diagnosis with gold standard tools," said Dr. Karl Kuban, chief of pediatric neurology at Boston Medical Center, who did not participate in the research.
The Centers for Disease Control and Prevention estimate that one out of every 100 eight-year-old kids has autism.
The new study, published in the journal Pediatrics, found that five out of every 100 young adults who was born weighing less than four and a half pounds had autism.
"Is it being born early that's leading to the problem, or is it that being born early and having autism share a common risk?" Kuban said. "We don't know."
The researchers followed several hundred premature babies from birth to 21 years of age.
Of the 189 young adults who went through an exam called the Autism Diagnostic Interview--Revised, 14 received an autism diagnosis.
"I was surprised," said Jennifer Pinto-Martin, a professor at the University of Pennsylvania who led the study.
Based on autism screens done during an earlier phase of this research, when the children were 16 years old, "I knew it would be higher than the general population...but I thought the rate would be about double," rather than five times as high, Pinto-Martin added.
The participants who had autism also had a high rate of other psychiatric disorders. Six of the 14 kids with autism had been diagnosed with another psychiatric disorder, such as phobias or attention-deficit hyperactivity disorder, at age 16.
Pinto-Martin and her colleagues did not show that being born early causes autism, but she said there is concern that prematurity puts babies' brains at a higher risk for injury, and perhaps that injury could have something to do with autism.
Her group is going back through ultrasound scans of the children's brains to look for possible signs of injury.
An earlier study in the UK and Ireland found that eight out of every 100 children born extremely prematurely -- before 26 weeks of pregnancy --developed autism (see Reuters Health story of February 11, 2011).
This rate is higher than what the current study found, probably because Pinto-Martin's group studied a broader range of preemies that included children born after 26 weeks of pregnancy.
She pointed out that when her research began in the 1980s, extremely premature babies were far less likely to survive than they are now.
"The profile of a low birth weight cohort today is going to look very different, and is likely to be filled with kids who have more risk," she told Reuters Health.
The vast majority of children born prematurely do not develop autism, and Pinto-Martin does not want her findings to alarm parents. "It's not something to worry about, but it's something to pay attention to."