Prenatal factors may play a role in autism

Mothers of children diagnosed with autism are more likely to be older and to have experienced obstetric difficulties during pregnancy, labor and delivery, but these complications are likely related to underlying genetic factors, according to an article in the June issue of the Archives of General Psychiatry, one of the JAMA/Archives journals.

According to information in the article, autism is believed to have a genetic basis, although some studies suggest that prenatal factors may play a role in this developmental disorder characterized by severely impaired social functioning and communication. Autism has a prevalence of about 10 to 20 per 10,000 individuals, and is usually diagnosed between the ages of 3 to 4 years, when certain developmental milestones are not met.

Emma J. Glasson, B.Psych., B.Sc. (Hons), Ph.D., of the University of Western Australia, Crawley, and colleagues examined the association between obstetric factors during pregnancy and birth, and autism spectrum disorders. The researchers studied obstetric information in the Maternal and Child Health Research Database of Western Australia for mothers who gave birth between 1980 and 1995, and whose children were diagnosed with autism spectrum disorders by 1999. The authors reviewed the medical information for children diagnosed with autism (n=465), siblings of children with autism disorders (n=481), and a random, population-based control group of children without autism (n=1,313), and compared obstetric information for the mothers of these groups.

The researchers report, "Compared with control subjects, cases had significantly older parents and were more likely to be firstborn. Case mothers had greater frequencies of threatened abortion, epidural caudal anesthesia use, labor induction, and a labor duration of less than one hour. Cases were more likely to have experienced fetal distress, been delivered by an elective or emergency cesarean section, and had an Apgar score of less than 6 at one minute [after birth]."

The researchers also found that the siblings of children with autism were more similar to their siblings than to the control group in terms of their profile of complications during pregnancy and birth.

The authors conclude, "The strongest findings were increased maternal age and a threatened abortion during pregnancy," the authors write. "It is unlikely that single factors or events cause autistic disorders, although it is possible that early nongenetic influences may act on the causal pathway for some cases. The observed complications are generally nonspecific and cannot predict autism development."