Causes of premature birth in puppies:

1. Genetic abnormalities in female dogs may cause premature uterine contraction, leading to premature birth.

2. Bacterial infection is one of the main causes of premature birth in bitches. Many bitches suffer from premature birth due to bacterial infection during pregnancy.

3. If the female dog is infected with canine parvovirus or canine herpes virus during pregnancy, the female dog is very likely to give birth prematurely or miscarry.

4. Female dogs may develop ovarian cysts, which can also lead to premature birth.

5. Various injuries may lead to premature birth in dogs, especially when the damage occurs around the uterus of the female dog.

6. Pregnant dogs may also have negative reactions due to stress in life, leading to premature birth.

7. Dogs with weak constitutions are prone to premature birth after pregnancy.