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Gestation for a dog is 63 days so you should not be seeing this (in regards XXXXX XXXXX) for a while yet.
But, yes, it is common for dogs to miscarry one or more puppies.
I suggest that you see the vet on Monday to have an x-ray done. This will let you know how many puppies to expect. Mom can also have an exam at that time to rule out pyoderma, a dangerous uterine infection.
Let me know if you still have questions.