By Anne Harding
Low birth weight and preterm delivery increase the likelihood that a child will be autistic, with girls being at particular risk, researchers from the US Centres for Disease Control and Prevention report.
"Pediatricians are probably sensitive to the fact that low birth weight children or children born too soon have special developmental needs," researcher Dr. Diana Schendel of the CDC's National Centre on Birth Defects and Developmental Disabilities, told Reuters Health.
"This study simply supports that they should not overlook the behavioural aspects of development."
She noted that while boys far outnumber girls in the general population of children with autism, physicians "may need to be aware that they will see more equal numbers of boys and girls" with autism among low birth weight and preterm children, based on the current findings.
Schendel and colleague Tanya Karapurkar Bhasin based their results on a comparison of 565 autistic children with 578 children the same age without the disorder. All of the children were born in the Atlanta area between 1981 and 1993.
The researchers found that among low-birth-weight and preterm children, autism was less common than other developmental disabilities, such as cerebral palsy and hearing or vision loss.
However, children born weighing less than 2 500 grams had about twice the risk of autism as those with a normal birth weight. Similarly, children born before the 33rd week of pregnancy were twice as likely to develop the disorder as those born at full-term.
Girls seemed to be particularly at risk.
Low-birth-weight girls were, for example, four times more likely to have autism accompanied by mental retardation or other developmental disabilities, compared with girls born at heavier weights.
The findings support the hypothesis that males and females have different causal "pathways to autism," the researchers write.
Girls, they speculate, may be more likely than boys to need a "prenatal insult" - such as poor growth - to set them on the path toward developing autism.
The researchers are investigating this and other hypotheses in the CDC's Study to Explore Early Development, a five-year study including roughly 2 700 children ages two to five. The study will be the largest collaborative investigation to date on the causes of autism.