MONDAY, Oct. 17 (HealthDay News) -- Low-birthweight babies are five times more likely to develop autism than normal-weight babies, a new study says.

It included 862 premature, low-birthweight infants born in New Jersey between October 1984 and July 1989 and followed until they were 21 years old. Their birthweights ranged from 500 grams (1.1 pound) to 2,000 grams (4.4 pounds).

Five percent of the children in the study developed autism, compared with 1 percent of those in the general population, the University of Pennsylvania School of Nursing researchers found.

The study appears online and in the November issue of Pediatrics.

Previous research has identified links between low birthweight and a number of problems with motor and cognitive skills, but this study is the first to show that low-birthweight children are also at increased risk for autism, according to the researchers.

"Cognitive problems in these children may mask underlying autism," wrote lead author Jennifer Pinto-Martin, director of the Pennsylvania Center for Autism and Development Disabilities Research and Epidemiology.

"If there is suspicion of autism or a positive screening test for ASD (autism spectrum disorders), parents should seek an evaluation for an ASD. Early intervention improves long-term outcome and can help these children both at school and at home," she said in a university news release.

Future research will examine possible links between brain hemorrhage (a common complication of premature birth) and autism. This will be done by examining brain ultrasounds of the children taken when they were newborns.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about autism.