> Although I have had 2 negative scans and both bitches gone on to whelp a litter.
This is what bothers me about all the scanning done these days. As I've mentioned (

) before, even if the scan says no, are you still going to cling to the hope that come the due date, puppies arrive? And even if a scan suggests there are puppies, that's only so at the time of the scan - there is no guarantee the bitch will carry to term. With a couple (or just one) of decent matings, plan for the litter and if nothing happens by the due date, THEN see your vet who will most probably x-ray, especially if he thinks the bitch is empty, to confirm.