Pregnancy factors, parental psychiatric history, and preterm delivery may be associated with an increased risk of autism, says a study in the American Journal of Epidemiology.

Here are the potential associations noted in the study:

--Breech presentation of the baby
--Low Apgar score, an index used to evaluate the condition of a newborn five minutes after birth
--Birth before 35 weeks of pregnancy
--Parental history of schizophrenia-like psychosis
--Parental history of affective disorder, which includes some psychoses, depression, and bipolar disorder

However, those traits are not presented as definite causes of autism or as the only possible risk factors for the condition. Of course, not all babies born under those circumstances have autism or related disorders.

'Possible Associations' Noted

"Right now, we have only identified possible associations," says CDC epidemiologist Diana Schendel, PhD, in a news release. "But if we can find a cause-and-effect relationship, it may help our efforts to prevent autism." Schendel worked on the study with other experts.

It's not known how those characteristics might interact with autism risk.

About Autism

Autism spectrum disorders are a group of developmental disabilities that are caused by unusual brain development, says the CDC's Autism Information Center. Some studies have shown that a rapid and excessive growth in head size during the first year of life may be an early indictor of autism.

The spectrum includes autistic disorder (infantile autism), pervasive developmental disorder, and Asperger's syndrome.

People with autism spectrum disorders tend to have problems with social and communication skills, and many have unusual ways of learning, paying attention, or reacting to different sensations, says the CDC.

The cause of autism spectrum disorders is not known. Studies on twins and families suggest that genetics may play a substantial role, the new study shows.

Autism Statistics

The study says between two and six per 1,000 children have autistic spectrum disorder, while autism specifically affects up to two per 1,000 children.

More children than ever before are classified with autism spectrum disorders. It's not clear if that's due to changes in identification or a true increase in the rates of the disease, says the CDC.

Probing Autism

The study focused on autistic disorder (autism), not other conditions in the autism family. Data came from Denmark's national health care system, which has records on virtually all children diagnosed with autism.

The study included every autistic child born in Denmark in the last 32 years and diagnosed before 2000. Each of the nearly 700 autistic children was compared with 25 kids without autism.

Parental psychiatric histories prior to the child's diagnosis of autism had the highest association with autism, says the study. Taking all the risks into account, parental psychiatric history increases the risk of an autism diagnosis by three- to fourfold. The authors do note that there have been genetic links found between schizoid personality traits and autism.

Autism was not associated with infant weight, number of previous babies born to the mother, number of doctor visits before pregnancy, parental age, or socioeconomic status.

Findings May 'Add to Evidence'

The study doesn't prove that events before and around birth are risk factors for autism, says a journal editorial.

However, the research "does add to the growing body of evidence suggesting that these events do occur more commonly among children with autism and that they should be studied further," write editorialists Craig Newschaffer, PhD, and Stephen Cole, PhD, of the Johns Hopkins Bloomberg School of Public Health.

CDC: New Study Is 'Helpful'

"This study is a helpful step forward in identifying possible risk factors for autism," says José Cordero, MD, MPH, in a news release. Cordero directs the CDC's National Center on Birth Defects and Developmental Disabilities.

"It also indicates that there may be some children for whom we need extra vigilance in watching for signs of developmental delay," he continues. "In recent years, many programs and studies have found that early recognition of autism is important because early treatment can significantly improve a child's development."

Treating Autism

Here's what the CDC says about treating autism spectrum disorders (ASDs):

"There is no known cure for ASDs. However, early and intensive education can help children grow and learn new skills. The goal of these efforts is to help with the difficult symptoms of an ASD in a child and to improve the child's skills that help him or her talk, interact, play, learn, and care for his or her needs. Medicines can relieve symptoms and be helpful for some people, but structured teaching of skills (often called behavioral intervention) is currently the most effective treatment."

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Larsson, H. American Journal of Epidemiology, May 15, 2005; vol 161: pp 916-925. Newschaffer, C. American Journal of Epidemiology, May 15, 2005, vol 161: pp 926-928. News release, CDC. CDC, Autism Information Center.