CHICAGO (Reuters) - One out of four toddlers born prematurely showed early signs of autism in a study, and the risk was greatest among those children who were the smallest at birth, Canadian researchers said on Wednesday.
Premature birth and low birth weight have been recognized in earlier studies as risk factors for a number of developmental problems, including autism and other illnesses.
But the study of 91 children, who were born around between 7 and 14 weeks prematurely and weighed 3.3 pounds (1.5 kg) or less at birth, was the first to directly assess the risk of autism in this population, the researchers wrote in the journal Pediatrics.
The initial screening test performed at around 21 months of age found suspected autism in 23 of the 91 children. The risk was greatest among those children who were the smallest at birth, and those born to mothers who suffered a prenatal infection or bleeding, Catherine Limperopoulos of McGill University said in a telephone interview.
"Early autistic behaviors seem to be an under-recognized feature of very low birth-weight infants," she wrote.
She added that the screening was preliminary, and definitive diagnosis would come in a follow-up study.
Autism or related disorders such as Asperger's syndrome strike one out of 150 U.S. children, the U.S. Centers for Disease Control and Prevention has estimated. The condition can have relatively mild symptoms or can severely disable a child by interfering with speech and behavior.
Higher rates of autism in recent years have been attributed to various causes, including improved diagnoses. Other studies have found genetic and other links to the condition, which many experts suspect may have several different causes.
Some activists believe childhood vaccines can trigger autism, though medical experts say they can find no such link.
Medical advances have greatly improved survival rates of premature and low birth-weight babies. But Limperopoulos and another expert said the study's findings did not mean the greater number of surviving premature babies was causing the increase in autism rates.
"I think this is not the answer to the increased rate of autism in our country, (though) it may well represent a small part of that increase. This is a more important finding for the world of prematurity than for the world of autism," said Dr. Alan Fleischman, medical director of the March of Dimes, a U.S. advocacy group that works to prevent premature births and birth defects.
The report said the findings do "support comprehensive screening for social and behavioral dysfunction in ex-preterm infants."
In a separate study in the journal, researchers at the University of Rochester in New York found families with an autistic child often faced financial hardship.
Besides having to pay more out-of-pocket for medical care and education, parents of the 131 children in the study with autism spectrum disorders lost an average of $6,200 from their expected annual income, or 14 percent.
Some parents opted for part-time work, because of limited community resources to help care for their children, the study concluded.
Editing by Maggie Fox and Mohammad Zargham