The bones of fetal puppies and kittens become mineralized (calcified) at around day 45 of their pregnancy. Radiographs taken of pregnant pets after day 45 of gestation will usually reveal whether or not the animal is pregnant because the radiographs will generally clearly reveal the skeletons of the fetuses.
Before this 45 day stage of the gestation, pregnancy diagnosis using radiography is generally inaccurate. The vet may get a subjective impression of an enlarged uterus, but this does not necessarily indicate that the animal is pregnant (other disease conditions besides pregnancy can produce enlargement of the uterus).
The advantages of abdominal radiography as a way of diagnosing cat pregnancy:
- Abdominal radiography is easy to perform;
- Abdominal radiography as a means of diagnosing pregnancy is accurate in dogs as well as cats, provided that it is performed at day 45 and beyond;
- Abdominal radiography can still be used to make a pregnancy diagnosis even in a very tense, resistant pet. Abdominal radiography can still be performed through even the most tense and tight abdominal muscles;
- It is usually possible to determine litter size with accuracy on abdominal radiography;
- If there are only one or two fetuses present, these are usually able to be detected on abdominal radiography;
- Radiography may be able to provide some indication of when medical and surgical intervention is required for a female pet giving birth (e.g. if the babies are too large in size to pass through the canal or if a large new coming baby appears to be stuck within the canal);
- Aging the fetuses is possible on abdominal radiograph;
- X-ray visibility and accuracy is not usually adversely affected by the presence of gas, feces or tissues within the abdominal cavity (unless the animal has been eating lots of bones – bony feces will interfere with the vet’s ability to spot and count the “bony” fetuses);
- The animal’s belly does not need to be shaved for radiography to be performed.
- Radiography is safe for the unborn babies, if done only sparingly.