Leonie I know for a fact that a child with ASD is more likely to have been born via c/section than an NT child.
However, that does not mean that c/sections 'cause' ASD (sorry not meaning to be patronising, just making sure it is clear for any lurkers etc.)
There is a 'theory' that having an ASD means that you are less able to participate in the mother-baby diad in an optimal cooperative way meaning that you are more likely to need medical intervention. This is no a theory I particularly agree with though.
If a birth is left totally undisturbed, the mothers body will flood with oxytocin, which will be passed onto the baby. This will continue to flow after the birth and until the cord has stopped pulsating. This hormone triggers the babies reflex to be alert and breasfeed and the mothers hormone to make her happy and bond which can only properly occur if the baby is given to her instantly and remains with her for the 'golden hour' and beyond.
Seperating mother and baby, cutting the cord before then and almost certainly filling both with drugs will stop the hormone from being produced in those enourmous quanitities and rob both mother and baby.
Additionally, fear and anxiety in the mother during pregnancy, and certainly during birth also inhibits the production of oxytocin and instead adrenaline which is the drug that makes us want to fight, flight and almost certain get away from people.
Imagine if you and your baby, were void of oxytocin, but flooded with adrenaline during the final stages of the birth and the first few hours?
Now I am not saying for one second that what I have described is the defining factor in ASD or not ASD. I very much doubt it is that simple, but I do believe there is something in it.
However, it is, as yet, an untested theory as far as I am aware (and I have been interested in this for a while and have searched and not found anything).