When detecting whether a dog is pregnant, multiple methods can be adopted, which are primarily based on physical changes and behavioral alterations of the dog.

Here are the detailed detection methods and steps:

External Observation Method:
Time: About 1 week after mating until before delivery
Observation content:
The genitalia begins to contract and soften, possibly accompanied by a small amount of dark brown liquid discharge.
Around 2-3 weeks of pregnancy, the breasts gradually enlarge, appetite increases, fur becomes shiny, temperament becomes gentle, and movement becomes slower.
After about a month, the abdomen swells, the breasts droop, the nipples are elastic, the mammary glands gradually enlarge, and even milk can be squeezed out. Weight increases rapidly, and the frequency of urination increases.
After 50 days, "fetal movement" can be seen on the side of the abdomen, and fetal heartbeat can be heard using a stethoscope on the abdominal wall.

Palpation Examination Method:
Time: Starting around 20 days of pregnancy, with the most suitable diagnosis time around 30 days
Procedure: Palpate the abdominal wall to perceive thickening of the uterine diameter. After 25 days of pregnancy, fetuses can be felt (such as touching an egg-sized, elastic fleshy mass).
Notes: During palpation, pay attention to distinguishing it from inelastic fecal masses. Use your hand to slide back and forth outside the abdominal wall above the last two pairs of nipples. Avoid excessive force or roughness to prevent miscarriage.

Ultrasonic Detection Method:
Time: Starting from 19-25 days of pregnancy, with an accuracy rate of 85% between 36-42 days of pregnancy, and 100% accuracy from 43 days to the end of pregnancy
Types: Doppler, A-mode ultrasound, and B-mode ultrasound. Among them, B-mode ultrasound has the best effect, able to detect fetuses from 18-19 days, and identify the gender, number, and viability of fetuses.

X-ray Examination Method:
Time: The shape of the uterus can be seen at 30-35 days of pregnancy, with significant changes in fetal bone structure at 49 days
Notes: Depending on the size of the female dog, 200-800 milliliters of carbon dioxide must be injected into the abdominal cavity.

Blood Test Method:
Time: Starting from 21 days of pregnancy
Principle: Determine pregnancy based on changes in blood components during pregnancy, especially the increase in pregnancy hormones such as relaxin.

Behavioral Observation Method:
Observation content: Whether the dog's behavior has changed, such as becoming quieter, more easily tired, clinging to people, as well as changes in appetite and abdominal shape.

Each of these methods has its own advantages and disadvantages, and they can be combined to improve detection accuracy. When suspecting that a dog is pregnant, it is best to take it to a veterinarian for professional diagnosis and advice. At the same time, pregnant dogs require special care and attention, including providing adequate nutrition and water, regular physical examinations, and preventive vaccinations.