A difficult birth or a history of mental illness in a parent may put a baby at greater risk for autism, according to a study that may provide clues to the causes of the devastating neurological disability.

The Centers for Disease Control and Prevention said on Monday that in a study of 698 Danish children with the developmental disorder, researchers found a disproportionately high number had been born before the 35th week of pregnancy, had suffered from low birth weights and were in a breech position at birth.

The children, all of whom were born after 1972 and diagnosed with autism before 2000, also were more likely to have a parent who had been diagnosed with schizophrenia-like psychosis before the autism was discovered.

The study was partly funded by the CDC and published in the most recent issue of the American Journal of Epidemiology.

Previous research had suggested that perinatal factors, parental psychiatric history and socioeconomic status might represent or include risk factors for autism. The CDC, however, noted that the latest findings did not indicate a definitive link between autism and troubled births or other possible risk factors.

“At this point we don’t know for sure if these events are causes, but it certainly points us to look more closely at what happens during pregnancy as a possible opportunity for future prevention,” said Diana Schendel, a CDC epidemiologist and one of the authors.

The study came amid growing debate in the United States over the causes of autism, which permanently impairs development of those areas of the brain that control verbal and nonverbal communication as well as social interaction.

About one out of every 250 babies in the nation is born with the disability, which usually appears in the first three years of childhood, according to the Autism Society of America.

Some parents have claimed that their children developed autism due to exposure to childhood vaccines containing the preservative thimerosal, an organic compound that is 49 percent mercury.

Thimerosal was used routinely in the United States between the 1930s and the 1990s to prevent bacterial and fungal contamination of a wide range of infant vaccines, including those for hepatitis B.

Thimerosal is no longer used in childhood vaccines in the United States, but remains in the influenza vaccine and in vaccines in other countries.

The CDC, which launched a campaign earlier this year to make doctors and parents more aware of the need for early diagnosis of autism and other developmental disorders, said it had found no proof of a link between autism and vaccines.