Ultasound scanning is commonly used in the UK to confirm pregnancy in dogs, cats and all small animals.
However, in the US there is a lack of trained ultrasound technicians and more specialist reproduction vets
who prefer to use X ray. Vets in the UK are reluctant to x ray a pregnant bitch for various reasons.

Here we look at the difference.

Can puppies be missed on an ultrasound?

Short Answer: yes
No diagnostic tool in medicine is 100%.

Why ultrasound a pregnant dog?

Short answer: for confirmation or if there is a medical concern about the litter.

From the owners perspective, most want the ultrasound done to confirm pregnancy very early. They don’t want to wait until day 42, or sometimes later as some vets prefer day 55 onwards for radiographs (x-rays).

Ultrasound are an excellent way to count fetal heartbeats and can be performed 28 days after the last time the bitch was mated.

Ultrasounds are extremely safe as opposed to x rays which should only be carried out in moderation.

If you are in the UK an ultrasound scan will cost from £20 with a professional ultrasound scanner, whereas in America for example, a scan can be around $500, and an x ray is cheaper. Reason is because they have far fewer professional ultrasound scanners and more reproduction vets who use x rays as opposed to ultrasounds.

When should you take an x-ray of a pregnant dog?

Short answer: after 42 days, most vets believe from day 55 onwards is safer

Long Answer: The timing of when we take an x-ray is really critical because depending on the stage of the pregnancy the bones of the fetuses might not be dense enough show up on radiographs. Fetal ossification occurs at about 42 days and on. So after this 42-day mark, you can see the fetus has most of the time on x-ray. However, before this date, you won’t see fetal skeletons and they will be missed. Most of the time if we are before the 42-day mark, you just see a big fluid-filled uterus on the x-ray and we don’t get to count the number of puppies.

Is it possible for puppies to be missed on X-Ray?

Absolutely it is. A quick search on social media will see people discussing x ray images of their pregnant bitch, all coming up with a different number. Medicine isn’t 100%. I have heard of people having X-Rays done on their apparently pregnant dog and not finding any fetuses. The most likely reason for this is that the x-rays were performed a little bit too early in the process of pregnancy. These numbers that I described above, the greater than 42 days number, are averages. Some pregnant dogs might have fetuses that develop slower than others, which could explain how they could be missed. Don’t blame your vet, medicine isn’t perfect.

What information do we gain from x-rays?

When taking the x-rays your veterinarian will also examine the pelvic bones to see about how large this is compared to the puppies. For example, If there is one gigantic puppy that is much larger than the pelvic canal, this might require a C-section. .

How accurate are x-rays?

Some believe X-rays are more accurate than ultrasound at counting puppies, but the x ray image doesn’t give an actual outline of the puppy so your vet has to interpret these images and make conclusions about how many fetuses are in there. X rays do not give finer details and you cannot see puppy heart beats.

There are many confusing elements to an x-ray. Vets uusually go about this by counting the number of skulls and then go back and count the number of vertebral columns, then they will add or subtract 1. For example, if a vet counts seven puppies they will usually tell the owner 7 puppies plus or minus one. This is because there can be puppies hiding in the images behind other puppies that sometimes they just can’t see. This is another reason why it’s good to have a veterinary radiologist involved to read the images as well.