Although the factors seem to act independently of each other, babies who were in a breech position at delivery, were more than five weeks premature, had a family history of schizophrenia, or had a low Apgar score five minutes after birth were found to be associated with an increased risk to develop autism later in childhood. The study is published in the May 2005 edition of the American Journal of Epidemiology.
"This is the largest case-control study ever conducted, and the first to suggest that family history of schizophrenia raises risk for autism, independently of obstetric factors," said William W. Eaton, PhD, study co-author and professor and chair of the Bloomberg School's Department of Mental Health.
The researchers examined data on 698 children who were born after 1972 and discharged from Danish psychiatric hospitals after a diagnosis of infantile or atypical autism through November 1999. Information on the children's parents was also obtained. The initial data was collected from nationwide registries in Denmark.
Dr. Eaton explained that previous autism studies used relatively small sample sizes, but that Denmark's extensive database for tracking the health of residents makes large population studies easier to complete.
Perinatal risk factors, such as mode of delivery, fetal presentation, preeclampsia and number of antenatal visits, were also investigated. Parental psychiatric history was ranked according to severity. Gross income of each parent, maternal education and parental wealth determined socioeconomic status.
The researchers did not find an association between risk of autism and the baby's weight, the number of children had by a woman, the number of antenatal visits, parental age or socioeconomic status.
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