could nyone tell me which is the best time to take a bitch to be scanned, and are they always accurate thanks

my vet scans aprox 28 days...not always accurate this year was told 5 and had 3 last years told 2 and had 4 ......

Scans aren't to predict numbers, just to confirm viable pups.  If you want numbers then your best bet is an x-ray, but this would have to be done later once the bones/skeletons had formed.