When whelping starts in dogs, all puppies are borne one by one. After the delivery of the first puppy, mother will have rest which can be of 15 minutes to 2 hours. After this rest, second puppy is born and again same process is repeated until complete liter is born. If mother still has puppies inside womb after delivery of few then wait for 2 hours maximum. If she does not deliver then take her to vet. This condition can be dangerous for both mother and puppy.