X-Rays vs. Ultrasound on Pregnant Bitches

Both radiographs (x-rays) and ultrasound have costs and benefits in determining pregnant dogs and puppy numbers. Both are equally prone to missing puppies, some of them are just sneaking about hiding!


- This is a very non-invasive means of looking at puppies. There is virtually zero risk to mom of the pups. The most accurate times for using ultrasound is between 18 and 25 days of pregnancy. Anything beyond 28 days loses accuracy because the horns of the uterus are beginning to twist and double-up on itself to accommodate the increasing size of fetuses. The accuracy in determining numbers of puppies is only as good as the skill of the ultrasonographer, but a good one should be +/- 1 pup. This is not a simple skill to learn, and most vets who are good at it have attended special training seminars to learn. Even then, it takes a lot of practice to learn how to take a 2-dimensional picture and turn it into 3 dimensions. We are blessed by having two of the best in the field here at the vet school. The advantages in doing ultrasound is that pregnancy can be confirmed at a much earlier time than even palpation. The dog simply has to lay quietly on her back and get a belly massage with warm gel. What corgi wouldn't love this!!! Viability of puppies can also be determined, by visualizing heart beats, age can be more accurately determined, by looking for key changes in the fetuses, such as intestinal motility, giving a better whelping date. Ultrasound can also identify empty sacs, indicating reabsorption of a fetus. Ultrasound close to whelping can identify some abnormalities, such as hydrocephalus, and skull sizes can be measured. The disadvantages of ultrasound is the cost and availability.


- Simple, readily available, less expensive than ultrasound. Greater risk to the developing fetuses during early gestation, so that alone is reason not to have them done before the last trimester. As someone already mentioned, the skeleton doesn't ossify (calcify) until after 47-49 days of gestation, so you have to wait until past this point before you have any hope of visualizing puppies. You can usually count puppies readily on radiographs, again +/- one puppy. (Count skulls, not spines!) Even here, someone can be hiding behind another puppy or along mom's spine. I have hunted for that last puppy after whelping and still not found him on radiographs, knowing he was there. The other advantage is that the skulls can be compared in size to the width of the dam's pelvis. I did a c-section on a bitch because she only had one puppy who was huge, AND he was pointed in the wrong direction. Now, he might have decided to turn himself around, but why take chances? The viability cannot be determined on radiographs alone. Unless a puppy has been dead for a long period of time, and is already decomposing, there is no way to determine is the skeletons you see on a radiograph belongs to a living puppy. The other big use for radiographs is as a quick check to determine if there is anyone still in the uterus after the bitch looks like she is done. Sometimes the contracting uterus feels so hard it resembles a puppy. I have heard of (not done, fortunately) c-sections on bitches without puppies, based on palpation, and I have certainly seen bitches who felt "empty" who had another puppy in the lobby or on the way home from the vet clinic.

So there you have it. What you use, whether you use anything at all, will be determined by your ultimate questions to be answered by the procedure, cost, availability and skill of the operators in question, and your veterinarian. I do not routinely x-ray or ultrasound every pregnant bitch, just the ones that I have questions or concerns about. Until returning to the vet school, I didn't have easy access to ultrasound without driving at least an hour. For simple pregnancy determination, I trusted my own palpation skills, which have proven to be quite accurate over the years on corgis.

Lyn Johnson DVM and the Tartan Corgi Crew
Texas A&M College of Veterinary Medicine
College Station, TX
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