If your dog has been mated by more than one dog during her cycle, it is possible for her to give birth to puppies who have different fathers. That is, depending on the breeds of dogs who may have mated your bitch, the puppies may look entirely differently from each other. I would recommend that the best option is to take your dog to your vet. He will be able to tell you whether your dog is pregnant at an early stage. If you do not want to do this, your dog will develop the following symptoms if she is indeed pregnant: enlargement of the teats and milk production, increased weight and the selection of a ‘nest’ or whelping site.