5 and a half weeks ago I mated my bitch with a proven stud. I had blood tests done so was aware she was likely to conceive, she is showing every early sign of pregnancy but today I had an ultrasound and there is no visible heartbeats or sacs. Is she likely to be infertile or is it common that even though all the right measures have been taken, she may not actually conceive?
Upsetting day

any advice will be greatly appreciated,
Thank you. I did have the Canine Herpes virus injection at 10 days after the last mating.