When a dog is ready to go into labor, she will lose interest in food for around 24 hours; she will also begin to lick its vulva and begin experiencing cramping in the abdominal region, according to PetMD. As the time for the pups to arrive draws closer, contractions will become more frequent and will occur around every 30 minutes.
Before the pups emerge, a shiny gray sac will droop from the vulva. This sac will look like a balloon. Some dogs may walk around while fluid drains from the sac, or may even open the sac on their own. Once the sac has appeared, pups will arrive within an hour. The dog may strain and moan as she pushes the pups out.