When do I need to worry if my pet's labor doesn't go well?

In a dog or cat that has never had a litter, hard labor should not last more than 2-4 hours.  A pet is in hard labor when having very hard abdominal contractions.  In a pet that has had a previous litter, hard labor should not last more than 2 hours.  Also, a dog or cat should not go more than 2 hours between puppies or kittens.  If labor is prolonged, or time between puppies/kittens is prolonged, your pet needs to see the veterinarian!