A dog can be in labor from two to 12 hours, states K9PuppyDogs.com. For first-time mothers, however, labor can last up to 36 hours. The birth of the first puppy generally takes the longest.
The Nest recommends watching for several telltale signs that birth is coming soon. A few days before labor begins, a dog's appetite decreases and her stomach becomes more bloated. About 12 hours to 24 hours before productive labor gets underway, a dog's temperature drops to between 98 and 100 degrees Fahrenheit. If labor does not begin within 24 hours after the temperature drop, a veterinarian should be consulted.