Not so much Aspergers, but more severe forms of austism, the study concertrated on several recreational drugs, but the most frightening, was when there was the use of amphetamines by the mother, and the strong correlation with this drug use and the most severe cases of autism in their children.
The study was done in Australia in 2005, I'm having a look to see if the data was posted online. Will post if I can find it.