Chances of having another child with ASD

Hi, i would like to know what the chances are of having another child on the autistic spectrum! I have a 9 year old daughter to my previous relationship who does not have autism and I have a son who is 4 who is on the autistic spectrum and me and my partner are considering having another child (my 3rd) but are slightly concerned of the chances of it been autistic , which my god I would still love the child dearly and would cherish it but don't know if we could cope with 2 children with ASD and concerned of how my son will cope with another sibling. 

Anyone found any latest research on the chances of another child been on the spectrum, any reply would be much appreciated. 

Thanks