Number Counting With Ultrasound

When it comes to sheep scanning, telling whether the ewe has a single lamb, twins or even triplets is important to the farmer. Even when scanning cows, it is important to take the time to check the full length of the uterine horns on both sides, to be sure you’re not missing a twin. DEFRA approved cattle scan training courses will teach not only how to scan the uterus, but also how to locate the ovaries, because two active corpus lutea can be a sign of potential (non-identical) twins. This is important knowledge for the farmer during calving, and also for the planning of his or her herd. If you’re skilled enough to be able to sex the calves, and have one male and one female, this is invaluable knowledge to the farmer as she or he can then prepare for the likelihood of a freemartin.

With canine and feline scanning, however, opinion on number counting is very much split. There can be no argument that ultrasound is highly ineffective when it comes to number counting, when compared with an imaging modality like x-ray. This is because, particularly in larger litters:

  • it’s very easy for one puppy to be obscured by another
  • ultrasound is a real-time imaging modality. The bitch is moving, the pups are moving, and the transducer is moving. Knowing which sac you’ve already seen and counted is very difficult – and with larger litters, impossible.

Having said this, almost all experienced scanners will be happy to give you a number range. Particularly if they’re scanning at the 30 day mark, where the sacs are smaller and it’s easier to discern one from the next, they may be comfortable in telling you that you can expect “more than 6” or “between 4-6,” for example. It’s important to realise that even this is not a fool-proof estimate; at this early stage, it’s perfectly normal for a bitch to resorb, so that all the puppies seen at the first scan may not continue to progress.

Foetal bone ossification occurs after day 40, with unequivocal pregnancy diagnosis possible with x-ray 43-54 days post-mating (Concannon & Rendano, 1983). At this stage, resorption will no longer occur, so you can be more confident that (in a normal healthy pregnancy) the number of puppies seen on x-ray will be the number of puppies born. At this stage with ultrasound, however, the puppies will often be so large that they are now overlying each other, making discerning one from the other very difficult.

In summary, if you are looking for a safe and effective way to receive confirmation of pregnancy in your bitch or queen, ultrasound is for you. If you’re expecting an unequivocal number count, you may be disappointed. Some AUA scanners will be confident enough to give you numbers with certain breeds, but be prepared to be given a range, rather than a definite confirmation.

 

Ultrasound X-Ray
Early (~30 days) confirmation of pregnancy Pregnancy cannot be confirmed until day 43 or later
Confirmation of viability at time of scan – scanner will check for movement of the foetus, and check the puppies’ heartbeats Provides a single snapshot in time. Cannot see puppies’ movement or heartbeats
No exposure to ionising radiation Exposure to ionising radiation
Performed with owner present, and may also be performed in the animal’s own home Performed at a vet practice, and owner cannot be present. Potentially more stressful
Cannot accurately confirm numbers Can provide an accurate number count
Usually costs around £40 Usually costs upwards of £100

 

References

Concannon, P., Rendano, V. (1983). Radiographic diagnosis of canine pregnancy: onset of fetal skeletal radiopacity in relation to times of breeding, preovulatory luteinizing hormone release, and parturition. Am J Vet Res 44(8):1506-11.

 

This article on dog pregnancy scanning and puppy counting was originally published on the 9th of June 2016. It was last updated on the 6th August 2017.