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!
Ultrasound - 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.
Radiographs - 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