Counting Puppies on Ultrasound – Understanding the Limitations

One of the most common questions owners ask during a pregnancy scan is:

"How many puppies are there?"

Whilst ultrasound is an excellent tool for confirming pregnancy and assessing foetal wellbeing, it is not a reliable method for obtaining an exact puppy count. Any indication of litter size should always be regarded as an estimate rather than a guarantee.

There are several reasons for this:

• Not all foetuses may be visible during the examination.
• One puppy can easily be hidden behind another.
• The bitch is moving, the puppies are moving, and the scanner is moving.
• Ultrasound provides real-time imaging rather than a static picture.
• Knowing which foetal sac has already been counted can be extremely difficult, particularly in larger litters.
• During the early stages of pregnancy, foetal reabsorption can occur.

For these reasons, even the most experienced ultrasound technicians cannot guarantee exact numbers. There is always someone who claims to know a scanner who "never gets the numbers wrong", but in reality no scanner possesses a crystal ball.

When scanning between approximately 28 and 35 days, it may be reasonable to provide a rough estimate such as "more than three" or "between four and six" puppies. Factors such as breed, previous litter sizes, body condition, and breeding history may help inform an estimate, but experienced scanners are generally far more comfortable providing a range than an exact count.

Foetal Reabsorption

One reason early puppy counts should be treated with caution is that not every pregnancy continues to develop exactly as first seen on ultrasound.

Foetal reabsorption is a natural process that can occur during the early stages of pregnancy. If a foetus fails to develop normally, the bitch's body may absorb the tissue without any outward signs.

In a normal pregnancy, the gestational sac appears as a dark, fluid-filled circle or oval containing a developing embryo. As pregnancy progresses, the embryo becomes increasingly distinct and a heartbeat can be identified.

When a pregnancy is failing or a foetus is being reabsorbed, the sac may appear:

• Smaller than expected for the stage of pregnancy.
• Irregular or collapsed in shape.
• Filled with cloudy or echogenic fluid rather than appearing completely black.
• Empty, with no visible embryo.
• Contain an embryo with no detectable heartbeat.
• Gradually decrease in size on repeat examinations.

Sometimes the sac appears completely empty. In other cases, remnants of embryonic tissue may still be visible within the fluid.

When Reabsorption Is No Longer Possible

Foetal bones begin to calcify at approximately 45 days gestation, sometimes slightly earlier. Once calcification has occurred, the foetus can no longer be reabsorbed by the body.

This is an important fact that owners should understand when discussing litter sizes and pregnancy scans. A puppy that has been visualised after calcification has occurred cannot later disappear through reabsorption.

If a puppy dies after calcification, several outcomes are possible. The foetus may become mummified and remain within the uterus until whelping, it may be aborted, or it may be retained. Whilst some mummified puppies cause no immediate complications, a deceased foetus can sometimes lead to inflammation, infection, premature labour, pregnancy loss, or compromise the health of both the bitch and the remaining puppies.

For this reason, any concerns regarding foetal viability should always be investigated by a veterinary surgeon.

Why Late-Pregnancy Counting Is Even Less Accurate

Many owners assume that counting puppies becomes easier as pregnancy progresses because the puppies are larger and easier to identify individually. In reality, the opposite is often true.

As the puppies grow, they occupy more and more space within the uterus. Whilst individual body parts become easier to recognise, it becomes increasingly difficult to visualise more than one or two puppies on the ultrasound screen at any given time.

By the final week or two before whelping, obtaining an accurate puppy count by ultrasound is generally impossible. The scanner may be able to assess foetal wellbeing by observing heartbeats, movement, and fluid surrounding the puppies, but reliably distinguishing and counting every individual puppy cannot realistically be achieved.

For this reason, late-pregnancy ultrasound should be viewed primarily as a tool for assessing viability and wellbeing rather than estimating litter size.

Every bitch is different. Some prefer to stand during the scan, others lie comfortably on their side, and some happily roll over to allow better access. These individual differences can further influence what can be visualised during the examination.

Why I Don't Give Puppy Numbers on Late Pregnancy Scans

A recent scan is a perfect example of why I am very cautious about giving puppy numbers, particularly when a bitch is scanned late in pregnancy. The owner had not realised his bitch had been in season but believed his male dog, who is her half-brother, may have mated her around a month earlier.

On scanning her, she was clearly and heavily pregnant and, judging by the size and development of the puppies, likely only had around two weeks left before her due date. At this stage it was also too late for Alizin or a planned spay/termination to be considered as an early pregnancy option.

The owner asked how many puppies she was carrying. I explained that I could clearly see two puppies lying side by side, but because she was so far into pregnancy I could not give an accurate number. The puppies were large and overlapping within the uterus, making it impossible to know whether I was seeing another puppy or simply coming back across one I had already counted. I said, “I can clearly see two, but she could have ten — it is impossible for me to guess accurately at this stage.”

Shortly afterwards, I discovered the owner had telephoned another client and told her that I had said the bitch was having ten puppies!

For clarity, I did not say she was having ten puppies. Ten was simply an example used to explain that, on a late scan, there could be considerably more puppies than the two I could clearly identify. This is exactly why I will not guess puppy numbers. If your bitch is scanned late in pregnancy, I can confirm pregnancy, assess what I can see at the time of the scan and may tell you the minimum number of separate puppies I can clearly identify — but that is not the same as a puppy count.

For the best chance of estimating numbers by ultrasound, scans should ideally be carried out between 28 and 35 days after mating or around 27–35 days after ovulation. Even then, ultrasound can never guarantee an exact litter size.

A Real-Life Example

One case has always stayed with me.

I scanned a bitch and identified what appeared to be a singleton pregnancy. As I routinely recommend with singleton pregnancies, I advised the owner to return for a follow-up scan so that we could monitor the pregnancy and confirm the findings.

The owner later cancelled the appointment and explained that they had sought a second opinion elsewhere.

The second scanner informed them that the bitch was carrying five puppies.

A further scan was then performed at approximately eight weeks gestation, and the owner was again told there were five puppies present.

When the bitch eventually whelped at nine weeks, she produced just one puppy.

Concerned, the owners contacted the scanner, who attended their home, charged for a third scan, and suggested that the missing four puppies had been reabsorbed after the eight-week scan.

This explanation is simply not possible.

By eight weeks gestation, foetal skeletons are fully calcified and clearly developed. Puppies supposedly identified at that stage cannot subsequently be reabsorbed before whelping.

This case perfectly illustrates why puppy counts should always be treated as estimates and why owners should be cautious of anyone claiming absolute certainty when counting puppies on ultrasound.

Ultrasound is an invaluable tool for confirming pregnancy and assessing foetal wellbeing, but it has significant limitations when it comes to counting puppies.

Early in pregnancy, some foetuses may not be visible and reabsorption can alter litter size. Later in pregnancy, the puppies become so large that counting them accurately becomes increasingly difficult and, in the final stages, often impossible.

For these reasons, ultrasound should be viewed primarily as a method of confirming pregnancy and monitoring wellbeing rather than providing an exact puppy count.

Any litter size given during an ultrasound examination should always be regarded as an estimate.

It is not uncommon for owners to be told that a precise number of puppies can be seen on ultrasound shortly before whelping. Whilst well-intentioned, such statements should be treated with caution. In late pregnancy, the puppies are simply too large and occupy too much of the uterus for accurate counting to be reliably achieved using ultrasound. At this stage, ultrasound is far more useful for assessing foetal wellbeing than attempting to determine exact litter size.