Ultrasound Versus X-ray
Ultrasound scanning is commonly used in the UK to confirm pregnancy in dogs, cats and other small animals. In some countries, X-rays are also used later in pregnancy, when the puppies’ skeletons have developed sufficiently to be visible.
Ultrasound and X-rays provide different information, but neither method can guarantee an exact puppy count.
Can puppies be missed on an ultrasound?
Short answer: Yes. No diagnostic test is 100% accurate.
Puppies can overlap, move or be positioned in a way that makes an accurate count difficult. The number seen during an ultrasound should always be treated as an estimate rather than a guaranteed litter size.
Why ultrasound a pregnant dog?
Short answer: To confirm pregnancy and assess the pregnancy at the time of the scan.
Many owners choose ultrasound because it can confirm pregnancy at a relatively early stage and allows fetal heartbeats and movement to be observed at the time of the scan.
An ultrasound can show fetal heartbeats and movement, depending on the stage of pregnancy and the position of the puppies. Pregnancy can usually be confirmed from approximately 28 days after the last mating, although dates may vary if the date of ovulation is not known.
Ultrasound uses sound waves rather than radiation and is generally regarded as safe when performed appropriately.
When can an X-ray be taken?
Short answer: The puppies’ skeletons may become visible on an X-ray from approximately day 42 to 45, although they are generally clearer later in pregnancy.
X-rays are not routinely used to confirm pregnancy in the UK. If there is a medical reason for considering one, your veterinary surgeon will decide whether it is appropriate and when it should be performed.
Can puppies be missed on an X-ray?
Yes. Puppies can overlap or be obscured by other puppies and structures within the abdomen, making individual skeletons difficult to distinguish.
If an X-ray is taken too early, the puppies’ skeletons may not have developed sufficiently to be clearly visible. Pregnancy and developmental dates can also vary, particularly when the exact date of ovulation is unknown.
What information can an X-ray provide?
An X-ray may show the puppies’ skeletons, their approximate size and their position at the time the image is taken. However, the image must be interpreted by a veterinary surgeon and cannot guarantee the number of puppies or whether a natural delivery will be possible.
How accurate are X-rays for counting puppies?
An X-ray does not provide a guaranteed puppy count. Puppies may overlap or lie behind one another, and different people may interpret the same image differently.
Unlike ultrasound, an X-ray does not show fetal heartbeats or movement. Ultrasound allows the operator to assess fetal heartbeats and other visible signs at the time of the scan, although any puppy count must still be regarded as an estimate.