My st bernard was artifical insamanated  now 28 days  no pups showed up on ultra sound can it be to early

Scanning which isn't necessarily accurate, only tells you yes, or no re a pregnancy, at the time of the scan.  I appreciate that sometimes getting a yes or a no is needed, but I'm not a supporter of scanning and prefer to wait.   By 7 weeks puppies should be seen moving around and even if a scan confirms a pregnancy, again there are no guarantees the bitch will carry to term.   IF I had this done, I'd still be watching by the due date, just in case

Depends on the experience of the person who scans. Many vets aren't as good at it as those who only scan, so best do it at around 32 days.

Agree with Goldmali ultrasound is only as good as person using it, my vet told me a funny story where at a practice where het friend works they were so bad an owner took the wand off them scanned her own dog then gave them a master class in using an ultrasound,  turns out she was a specialist ultrasound nurse at local General hospital

The trick is definitely to find an experienced scanner, I remember making an enquiry about scanning with my vets (it was my first litter) - they told my they've got the scanning equipment but no one is quite sure how to use it Suffice to say, I wasn't willing to let my girl be their guinea pig. Since then, I have only used an experience scanner and do so with every litter

Their is poster up in my vets saying they have ultrasound specilist
its worth asking if they have specilist or can refer you to one