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Detecting Dog Pregnancy: Ultrasound vs X-ray

Detecting Dog Pregnancy: Ultrasound vs X-ray

By Ines Di Giacomo DVM

When we decide to mate our dogs, we have to consider many aspects of future pregnancy: diagnosis, nutrition, monitoring, birth and the management of the litter. We will discuss these topics again, but now we will focus on how and why it's important to make a diagnosis of pregnancy in our dogs. An early and certain diagnosis of pregnancy allows optimal management of our dog. There are three main methods for diagnosing pregnancy in dogs: palpation, ultrasound and X- ray. Obviously, all three methods must be made by a qualified veterinary to avoid, in the best of case an incorrect diagnosis, in the worst possible damage to embryos, in particular with a wrong palpation.

Detecting Dog Pregnancy By Palpation

Palpation can be made from 23 to 30 days after ovulation, so very early. Sometimes palpation is difficult with overweight or very muscled dogs.

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Moreover, the number and the vitality of the fetuses can not be determined with accuracy.

"Remember: the gestation period in dogs is calculated from ovulation to birth, not from the date of breeding! And it is 63 days ±1 in 55 percent of cases, 63 days ±2 in more than 85 percent of cases."

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Detecting Dog Pregnancy by Ultrasound

This is the reference examination. It can be done from 21th day after ovulation. It's a simple execution technique, since it does not require that the patient be subjected to anesthesia and does not cause pain or discomfort to the patient and can be performed in the presence of the owner.

Technically, it runs through the aid of ultrasound probes that emit ultrasound which are processed and translated into visible images in real time on a computer screen. The ultrasound allows the evaluation of the viability of the fetus, through the evaluation of fetal movements and fetal heart rate, as well as the prediction of the birth date, through the measurement of fetal and extrafetal structures.

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When the estimation of the number of puppies is performed by ultrasound it's a good idea to recommend a radiographic check at the end of gestation. Indeed, fetal reabsorptions and abortions can alter the number of puppies that reach the end of pregnancy.

"The number of fetuses often is underestimated, except in small breeds. From 10% to 15% of embryos is reabsorbed spontaneously before 30 days, especially in large size female and in large litters."

Ultrasound allows to evaluate the first fetal heart movements, fetal movement, fetal heart rate and to establish the vitality of the fetus. The age of the fetus is determined by ultrasound considering first the appearance of some visible structures than by measuring certain parameters.

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By ultrasound you may obtain measurements of certain structures, such as for example the length of the diameter of the gestational sac (GSD, Gestational Sac Diameter), the crown-rump length (CRL, Crown-Rump Length), the diameter of the fetal head (HD, Head Diameter) and the diameter of the body of the fetus (BD, Body Diameter), which relate closely to the age of the fetus and allow to estimate the duration of gestation and the birth date.

"The size variations related to breed, the differences between the brachycephalic breeds and individual variation in measurement technique, are sources of inaccuracy in predicting fetal age by ultrasound."

Detecting Dog Pregnancy by X-ray

dog xray

The radiographic image is a two-dimensional gray-scale reproduction of the three-dimensional anatomical structures. It's the most accurate method for determining the number of fetuses, being able to count the heads and/or the spine of the pups. It can be done from the 50th day.

In contrast with ultrasound, x-ray imaging provides limited information about gestational age and vitality of fetuses. In fact, the evocative images of fetal death are related only to postmortem alterations in fetuses, as intra-fetal gas accumulation, abnormal postures, overlap of the cranial bones.

Radiographic examination is the most accurate method for the correct estimation of the number of puppies, especially if performed in proximity of birth, when the state of calcification of fetuses is advanced.

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"Fetal mineralization, the definitive radiographic sign of pregnancy, does not occur before 45-50 days (according to different authors) after ovulation."

X- ray can also be used for the identification of some pelvic abnormalities that could increase the risk of dystocia. Dystocia is difficult birth that requires obstetrician intervention, manual or instrumental, with danger to the life of the mother or fetus. It would be advisable not to feed the dog in the 12 hours before the test, to avoid confusing the fetuses with gastrointestinal contents.

The Bottom Line

So if you are still wondering if it would be appropriate to do an ultrasound or an x-ray or both of your pregnant dog, consider that the ultrasound examination is the earlier and accurate investigation for the diagnosis of pregnancy, while the radiographic examination in proximity of the end of pregnancy is the technique of choice for the evaluation of the number of puppies. Ask your vet what is the best diagnostic procedure for your case.


  • “Manuale per il veterinario – Pediatria e medicina della riproduzione”, A. Fontbonne
  • “Trattato di ecografia del cane e del gatto”, J. Mattoon, T. Nyland, 3° ed., Edra-EV, 2016
  • “Medicina interna del cane e del gatto”, C.G. Couto, R.W. Nelson, 5° ed., Edra-EV, 2015
  • “Diagnosi e management di gravidanza: tempi e modi della determinazione della data del parto”, M. Beccaglia DVM, Dipl. ECAR, 68° Congresso Nazionale Scivac, 2011

About the Author

Ines Di Giacomo DVM graduated from the Faculty of Veterinary of the University of Teramo, in Abruzzo Italy. She's interested in ultrasound diagnostics so decided to follow a specialist so to learn more about this topic.

ines di giacomo

In the meanwhile, she has been attending a veterinary clinic to put into practice what she has learned during her years of study. Since her graduation, Ines has attended numerous seminars to improve her knowledge in different areas of veterinary medicine such as radiology, ultrasound, reproduction, dermatology.

Ines would love to expand her knowledge in parasitology, anethesiology, and surgery but the road is still long. She says "Although the university is over, you never stop learning!"

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