The main methods for detecting pregnancy in dogs include the following:

I. Observing Physical Changes

• Mammary Gland Changes: Early in pregnancy, a dog's nipples will enlarge and become more prominent. As pregnancy progresses, they will become fuller and swollen, and occasionally, a liquid may discharge from them.
• Abdominal Changes: In the initial stages of pregnancy, a dog's abdomen may become more rounded and bloated, feeling firmer and tighter. As time passes, the abdomen will expand further, and one may be able to feel fetal movements upon touch. Particularly during the last three weeks of pregnancy, the dog's belly will be round and swollen, and its mammary glands will swell due to hormonal changes.

II. Observing Behavioral Changes

• Behavioral Abnormalities: In the final three weeks of pregnancy, with the bulging belly making movement more challenging, dogs tend to sleep more than usual. They may also become more docile and affectionate towards their owners or exhibit other unusual behaviors, such as restlessness or discomfort.
• Nesting Behavior: As the birthing time approaches, dogs may display nesting behavior, preparing a warm, cozy, and safe nest for their puppies. This nesting behavior can occur anywhere from 2-3 days to even 2-3 weeks before delivery.

III. Professional Detection Methods

• Abdominal Palpation: Around 20 days after mating, abdominal palpation can be performed for early diagnosis. By day 30, a sense of tension may be felt upon palpating the abdomen. By day 50, as the fetuses grow, one may be able to palpate the fetuses in the posterior part of the uterus. However, this method requires experience and skill, and its accuracy can be affected by the dog's body type and abdominal fat.
• Ultrasound: Ultrasound can be used after 27 days of pregnancy to determine the number of fetuses. As the fetuses grow, ultrasound can provide clear images of their movements and sizes within the uterus. This method is highly accurate for early pregnancy diagnosis and determining fetal count.
• Radiography: After 42 days of pregnancy, radiography (such as X-ray) can be used for diagnosis, which can also help differentiate between true pregnancy and false pregnancy. However, it should be noted that radiography poses a certain radiation risk to both the dog and its fetuses, so it is not typically the first choice for detection.
• Blood Test: Detecting pregnancy hormones (such as relaxin) in the dog's blood can confirm pregnancy. This method is highly accurate and reliable but requires professional veterinary handling.

IV. Other Considerations

• Avoid Early Increase in Food Intake: It is important not to increase the dog's food intake too early. The correct time to increase food portions is during the last three weeks of pregnancy.
• Regular Health Checks: Regular veterinary check-ups and prenatal examinations are essential during pregnancy to ensure the health of both the dog and its fetuses.
• Nutrient Supplementation: Adequate nutrition, including proteins, fats, vitamins, and minerals, is crucial during pregnancy. However, it is important to adhere to moderation to prevent excessive weight gain that could complicate delivery.