In The Politics of Autism, I discuss various ideas about what causes the condition.
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.
Spacing pregnancies in close succession may increase the risk of autism in children, a large new research review suggests.
Examining existing research involving more than 1.1 million children, scientists also found that longer pregnancy spacing -- in excess of five years -- may be linked to raised odds of the increasingly common neurodevelopmental disorder.
"Based on the current best available evidence, it appears that the ideal interpregnancy interval -- the time elapsed between the birth of the immediate older sibling and the conception of the younger sibling -- is 2 to 5 years, in order to reduce the risk of autism," said study author Dr. Agustin Conde-Agudelo. He is a researcher at the World Health Organization Collaborating Center in Human Reproduction at the University of Valle in Cali, Colombia.
"The reasons for the association between short interpregnancy intervals and autism and other neurodevelopmental disabilities are unknown," added Conde-Agudelo. He noted that scientists believe nutrition and other factors may play a role.
However, the study doesn't prove that either long or short intervals between pregnancies actually cause autism, just that there seems to be an association.