As the diagnosis of autism spectrum disorder (ASD) has become increasingly common throughout the world, it has been noted that, unlike many other diseases, autism is diagnosed at a higher rate in children whose families are of high socioeconomic status (SES). Amongst other factors, It has been most popularly hypothesized that children born to more affluent parents develop autism at higher rates due to their parents likely being older.
However, a 2004 study that analyzed the records of 698 Danish children born after 1972 who developed autism before 1999 found that neither SES or parental ages were statistically significant risk factors for autism spectrum disorder. Rather, parental psychiatric history, specifically schizophrenia-like psychosis, was most strongly associated with the development of autism in children, presenting a Risk Ratio of 3.44. The strong correlation between parental psychiatric history and autism in children suggests a genetic component to the development of ASD in children. This genetic link has been validated through many molecular genetic studies (Hartwig, 2019). Other factors that were statistically significant in their associations with ASD were gestational weight at birth, a low Apgar score 5 minutes after birth, and being born in the breech position. While it is not clear exactly how the latter components affect the development of autism, it appears that birthing circumstances and neonatal birthing-readiness are important in the neurodevelopment of children.
Due to the strong association between ASD and parental psychiatric history, in acknowledgment of the other studies that have pointed to SES and parental age as factors, it could be suggested that parental psychiatric history may be related to the age in which adults may decide to have children. Especially in women, schizophrenic symptoms tend to manifest later in life. Psychiatric conditions may delay the start of a family for some individuals, leading them to be older and further along in their career when they have a child. The interactions between genetic and environmental factors are not completely understood, and the array of genetic and environmental factors that appear to affect the development of ASD suggests that additional investigation must be done to determine the effects of confounding variables on the development of ASD.
Larsson, H. J., Eaton, W. W., Madsen, K. M., Vestergaard, M., Olesen, A. V., Agerbo, E., ... & Mortensen, P. B. (2005). Risk factors for autism: perinatal factors, parental psychiatric history, and socioeconomic status. American journal of epidemiology, 161(10), 916-925.