Here are some possible explanations:
1. Small Litter: It is not uncommon for dogs to have small litter sizes, and some pit bulls may have only one puppy.
2. Pregnancy Loss: Sometimes, a dog may lose one or more puppies during pregnancy due to various factors such as genetics, health issues, or environmental factors. If the other puppies were reabsorbed or miscarried, it could lead to a singleton litter.
3. Dystocia: Dystocia is a medical condition in which labor becomes slow or difficult, potentially causing the delivery of only a partial litter. In such cases, the remaining puppies may be born much later or may require veterinary assistance for delivery.
4. Miscounting: There might have been a counting error during the birthing process, and it's possible that there are additional puppies yet to be born.
5. Incomplete Labor: In rare cases, a dog's labor may pause after delivering one puppy and resume later. It is essential to monitor the mother closely in these situations to ensure the well-being of any additional puppies.
If you are concerned about the size of the litter or if the labor seems incomplete, it is crucial to consult with a veterinarian promptly. Regular monitoring, especially in the early stages of labor, can help identify potential problems and ensure a successful birthing process. The veterinarian can provide appropriate care, guidance, and treatment if necessary.