The appearance of a pregnant dog's belly can vary depending on the breed, size, and number of puppies she is carrying, as well as the stage of pregnancy. In the early stages of pregnancy, a dog's belly may not look noticeably different, but as the pregnancy progresses, some changes may become apparent. Around 4-5 weeks into the pregnancy, the dog's belly may begin to show some swelling and appear slightly rounder. As the puppies continue to grow, the belly may become larger and more visibly distended. The nipples may also become more prominent and enlarged as they prepare for milk production. In the later stages of pregnancy, typically around 8-9 weeks, the belly may become very large and firm to the touch. The dog may also appear uncomfortable or restless and may exhibit nesting behavior such as digging and rearranging her bedding.