Babies born with a low birth weight are five times more likely to be diagnosed with autism than those born at a normal weight, according to an American study published Monday.

Researchers at the University of Pennsylvania School of Nursing followed 862 children who were born in New Jersey from 1984 to 1987, each weighing between 500 grams (17.6 ounces) and two kilograms (4.4 pounds), for a period of 21 years.

The study, published in journal Pediatrics, found that five percent of the children studied were diagnosed with autism, compared to one percent of the general population.

Lead author Jennifer Pinto-Martin said, "As survival of the smallest and most immature babies improves, impaired survivors represent an increasing public health challenge. Emerging studies suggest that low birth weight may be a risk factor for autism spectrum disorders (ASD)."

Links between low birth weight and a range of motor and cognitive problems have been well established for some time, the researchers said, but this is the first study establishing that low birth weight babies are also at increased risk for ASD.

"Cognitive problems in these children may mask underlying autism," Pinto-Martin said. "If there is suspicion of autism or a positive screening test for ASD, 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."