Here is just a partial list of correlates, risk factors, and possible causes that have been the subject of serious peer-reviewed studies:
• Air pollution and proximity to freeways;
• Maternal thyroid issues;
• Autoimmune disorders;
• Induced labor;
• Preterm birth;
• Birth by cesarean section;
• Maternal and paternal obesity;
• Maternal and paternal age;
• Maternal post-traumatic stress disorder;
• Smoking during pregnancy;
• Antidepressant use during pregnancy.
I also write: "If the science were not confusing enough, its coverage in the mass media has added another layer of murk. News reports hype tentative findings and weak correlations as “breakthroughs” in the quest for autism answers. " One recent example is the notion that too much folic acid may play a part.
Another involves circumcision. Sarah Kovac reports at Time:
Dr. Morten Frisch is a Danish epidemiologist who led a study examining the link between circumcision and ASD. The study, published in the Journal of the Royal Society of Medicine, found that boys who undergo circumcision are more likely to be diagnosed with autism by age 9. “Considering the widespread practice of non-therapeutic circumcision in infancy and childhood around the world,” the study states, “confirmatory studies should be given priority.”
But Frisch’s study is not without its critics, one of the most vocal being Professor Emeritus Brian Morris of the University of Sydney. “The problem with Frisch’s fundamental premise is that circumcision causes pain in infants and boys… Sometimes observers believe that crying during a circumcision is because of pain when in fact it is more likely because of the baby having to be restrained.” Morris also points out that, in many circumcisions, the baby doesn’t even cry during the procedure, and may even fall asleep.
His argument is supported by statistics out of Australia, where circumcision rates have been dropping since the 1960s, but ASD diagnoses have been rising.