After breeding, a female dog has a gestation time that can last anywhere from 55 to 66 days. After the 40th day, her breasts will enlarge noticeably and she will begin to put on weight. According to "Dog Owner's Home Veterinary Handbook" (Debra M. Eldredge, DVM, et al, 2007), many pregnant dogs will experience morning sickness as early as the 28th day, but not all pregnant dogs will get morning sickness. The mother dog then looks for a dark, soft, quiet place in order to give birth, or whelp. She may pick the place out a couple of weeks before labor begins. Twelve to 24 hours before labor, she loses her appetite and becomes very restless. The entire whelping process where the puppies come out through the vagina, takes an average of six to 12 hours. If another pup is on the way, the mother dog will begin to strain from five to 30 minutes after whelping the last puppy. The mother dog normally eats the afterbirth and severs the cord herself.
Several breeds of dogs have problems giving birth vaginally and usually need to have a Caesarian section. These breeds include narrow-hipped dogs such as the bulldog, Boston Terrier, Pomeranian, Vizsula, toy poodle and Chihuahua. Dogs suffering from uterine rupture, dystocia or another medical problem may also need a Caesarian if the puppies and the mother have any hope of surviving. This procedure is done under general anesthesia to open up the uterus and remove the puppies and placentas manually. The belly area of the mother is shorn. When the puppies are removed, the dog can also be spayed if that is wanted. Mother dogs can often wake up to take care of the puppies in as little as three hours.
Many dogs are able to whelp without any help from people, but a vet needs to be contacted as soon as possible if the mother has been straining for an hour without a puppy showing. It could be lodged in the birth canal. It is most likely dead and all of the other puppies will soon be as well unless the dog is taken to a vet. Even if there is a sac or a membrane showing for more than 15 minutes but still the puppy isn't moving, call the vet. Dogs that pass a green fluid or pass a lot of blood before any puppies appear also need to see the vet.