Canine gestation lasts an average of 63 days, although it's normal for dogs to deliver a few days before or after that time. If you bred your dog, you have a good idea of her due date. Veterinarians can calculate the approximate due date of dogs with an unplanned pregnancy.
Your vet can palpate your dog's abdomen to determine if there's a pregnancy about three weeks after the breeding. At that point, the embryonic vesicles that will develop into puppies are about 1 centimeter long. To your vet, they feel like walnuts within the uterus.
Ultrasounds and X-Rays
A more reliable way of confirming canine pregnancy is via ultrasound. At about the third week, the vesicles are visible on an ultrasound. The earliest that an X-ray can determine pregnancy is about day 39, or just more than five weeks into the pregnancy. The actual number of puppies can't be calculated by X-ray until just about a week before the due date. That's when the skeletons mineralize and can be seen clearly on a radiograph.
A day or so before birth, or whelping, your dog might start dripping milk from her teats. As early labor begins, she becomes restless and might exhibit nesting behavior. She won't eat at this time, but provide her with water. Early labor lasts between six and 12 hours. The next stage of labor heralds the arrival of the puppies.