Research suggests that heredity and early fetal development play a causal role in autism.
An analysis conducted by researchers at the Aarhus University in Denmark, Johns Hopkins Bloomberg School of Public Health and the Centers for Disease Control and Prevention ( CDC ), explored the association between perinatal factors, parental psychiatric history, socioeconomic status, and risk of autism.
Children 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.
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, of the Bloomberg Schools 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 childrens parents was also obtained.
The initial data was collected from nationwide registries in Denmark.
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 childs weight, the number of children had by a woman, the number of antenatal visits, parental age or socioeconomic status.
Source: American Journal of Epidemiology, 2005