Anyone know of things during pregnancy that cause SPD?

I'm just curious if anyone is aware of anything that you could do while pregnant that could possibly cause SPD in the baby? Can listening to loud music? Not taking the prenatal vitamin like you are suppose to? Iron deficiency? Being too active? Drinking too much caffeine? Hair dye? Etc. etc.

I have a two year old with SPD and we are considering having another child but I fear having another child with the same disorder. I just wondered if there was anything I could have done while pregnant with my first child to have caused the SPD so I can make sure not to do that with the second child. Any valid thoughts on this would be helpful? Thanks!