Ultrasound is used to confirm pregnancy in both dogs and cats. Typically, you are able to see the developing fetuses starting 25-28 days. Ultrasound is usually recommended between 28-30 days for the best chance for seeing if she is pregnant. At this time, you can see the baby’s heartbeats and some developing characteristics as well as evaluate for any unforeseen problems. At this ultrasound the number of puppies can be predicted along with a due date.
Sometimes owners would like to have a more definite count. If this is desired, a flat film x-ray is recommended usually 1 week prior to due date. This allows the doctor to count the number of skulls and skeletons, but even this is still an estimate. This is also used for estimating puppy size compared to the pelvic size to make sure she is able to deliver them on her own without surgical assistance.