Here's why:
* Heat cycles are controlled by hormones. A dog's heat cycle is triggered by hormonal changes.
* Pregnancy also involves significant hormonal changes. These changes are different from those that cause a heat cycle and actually suppress the hormones responsible for going into heat.
* Pregnancy overrides heat cycles. While a female dog might be in heat when she becomes pregnant, the pregnancy will stop further heat cycles until after she gives birth and weans her puppies.
Important note: It's crucial to ensure your dog is properly cared for during her pregnancy. Consult with your veterinarian for advice on diet, exercise, and other aspects of prenatal care.