
Hi Sally,
Loads of factors:
How high are you on the waiting list?
What does the breeder intend to keep?
Have you specified male or female?
Do you want a particular colour in a possibly multi-coloured litter?
What breed of dog/what size of litter do they normally have?
So, answer is possibly of the 'how long is a piece of string' variety! If you're waiting for an Irish Setter or Rottweiler, with large litters and no colour variations, chances are good - if you're waiting for a female rough-coated Griffon Bruxellois, not so good!! Suspect you'll be somewhere in between.
M.