The possibility of intrauterine infections as a plausible explanation for the increased autism prevalence in children born to immigrant mothers is relevant. Hypothetically, mothers arriving from a totally different culture may not have been exposed to the same type of infections as have native mothers. This explanation would only hold if the mothers had lived in the immigrant country from at least the second trimester (the period during which infection by agents to which the mother is not immune would damage the brain in ways which would lead to autistic symptomatology). This applied in all three cases in the present study. [pp. 143-4] (Gillberg, C., Schaumann, H. & Gillberg, I. C. (1995). Autism in immigrants: Children born in Sweden to mothers born in Uganda. Journal Of Intellectual Disability Research: JIDR, 39(Pt. 2), 141-4.)
Season of birth effects have the potential to make clearer the cause of autism in equatorial populations migrating to Northern climes. If those with autistic tend to be born in certain months, several etiologies are suggested.
One in the Vitamin D hypothesis. Another is the influence of the pineal gland on testosterone levels.
Related in the possibility that allergies are causing autism, allergies in a pregnant mother. How to allergies influence testosterone levels? Do the stress they cause increase testostesterone levels? Are children conceived at certain times more vulnerable to autism when mothers are highly allergic in the fall?
If maturation rates are set at a specific time in gestation, what influences testosterone levels at that time may be encouringing autism. How much effect does infection and allergies have upon uterine testosterone levels?