Pregnancy can be confirmed from 28 days after the last mating and although I have seen puppies from as early as day 24, optimum results are achieved from around day 32 - 35 of your bitch's pregnancy. I can also scan well behaved cats.
Scans performed in my own or yours (different rates apply for mobile)
Please note that any indication of numbers is an estimate as re absorption can occur and not all foetuses may be seen. It is very easy for one puppy to be obscured by another. Ultrasound is 'real time' imaging, the bitch is moving, the puppies are moving and the transducer is moving. Knowing which sac you have already seen and counted is extremely difficult, and with large litters, impossible!
There is always some one who knows a scanning technician who never gets the numbers wrong. However, this is purely guess work based on knowing the breed, the bitch and other bits of history they can glean from you on the bitch and although they have a crystal ball, they do get it wrong.
Most experienced scanners are happy to give you a number range. Particularly when scanning around the 30 day mark, where the sacs are smaller and it is easier to discern one from the next. We are usually comfortable in telling you that you can expect "more than 3" or "between 4-6," for example. It's important to realise that even this is not a fool-proof estimate as in the early stages, it's perfectly normal for a bitch to resorb, so that all the puppies seen at the first scan may not continue to progress.
Calcification of foetal bones is around day 45, but can sometimes be seen earlier. Some bitches prefer to stand, some will lie down on their side, and some will oblige by rolling over, each bitch is individual. The further along the pregnancy the better the images, but the less likely you can see more than one or two puppies at any one time due to the size of the foetus.
I also offer a FREE still image or video of your experience via email.