The study is "another indication that there may be something going on very early in these kids' development...before they're born," said George Delavan, director of the state's Division of Community and Family Health Services and co-principal investigator.

The study examined the births of nearly 5,000 Utah children, drawing on the same data used in an autism prevalence study released Thursday. The children's medical and school records were linked to birth data, which revealed:

- The mean weight of children with autism was 7.03 pounds, while the mean weight for children in the general population was 7.35 pounds.

- 9.7 percent of the children with autism were in breech presentation at birth, versus 4.1 percent of the general population.

- About one-fifth of children with autism were born by C-section, while 9.2 percent of the general population was born this way.

"One way to think of it is, it's sort of the baby's responsibility to get in the right position to be born," Delavan said.

If the baby doesn't, it could be indicative of a neurological or anatomical defect, or "sort of subtle early indications of problems," he said.

Similar findings were published in 2005 in the American Journal of Epidemiology. That study showed factors associated with autism include breech presentation at birth; delivery before 35 weeks; and a parent diagnosed with a schizophrenia-like illness before the child was diagnosed with autism.