Pregnancy Testing in the Dog

By Krista Williams, BSc, DVM, CCRP; Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DVM, DVSc

Is there a blood test to detect pregnancy?

Yes. The blood test detects pregnancy in the pregnant dog by measuring levels of a hormone called relaxin. This hormone is produced by the developing placenta following implantation of the embryo, and can be detected in the blood in most pregnant females as early as 22-27 days post-breeding. The level of relaxin remains elevated throughout pregnancy, and declines rapidly following the end of the pregnancy.

Can the relaxin test tell the difference between pregnancy and pseudopregnancy?

Pseudopregnancy (pseudo = false) is a trick of nature that causes a female dog to look and behave as if she is pregnant even though she is not. The signs appear for about two months immediately after a heat period.

There is no actual placental development during pseudopregnancy, and relaxin is not produced at any time. The relaxin test will always be negative in the pseudopregnant dog and can be used reliably to tell the difference between pregnancy and pseudopregnancy.

Does a single negative relaxin test mean a female dog is not pregnant?

Any negative result may indicate that a female dog is not pregnant. However, a false negative result may occur if the test is performed too early in pregnancy, before the placenta has started to produce relaxin. A dog that is negative for relaxin on the initial test, performed at 22-27 days post-breeding, should be tested again one week later to confirm the negative results. Doing multiple tests is especially important in the early stages of pregnancy and whenever the breeding dates are unknown.

"A false negative result may occur if the test is performed too early in pregnancy."

In most cases (80% of the time), two consecutive negative relaxin tests one week apart, starting 22-27 days post-breeding, confirm that a dog is not pregnant. Rarely, a third test at 31-34 days post-breeding may be needed if breeding occurred very early in the heat period. There is also evidence that dogs of small and toy breeds may not produce enough relaxin to turn the test positive, especially if they are carrying only one or two puppies. In these females, alternative testing is used to determine if puppies are present (see below).

Does a positive relaxin test mean a dog is pregnant?

A positive relaxin test indicates that a dog is pregnant at the time of the test - conception has occurred, implantation of an embryo has taken place, and a placenta is developing.

Does a positive relaxin test mean that live puppies will be born?

Not necessarily. A positive relaxin test indicates only that a dog is pregnant at the time of the test. It does not predict that the pregnancy will end successfully with the delivery of live puppies.

 Unfortunately, there are many reasons why pregnancies fail, and fetuses can be lost at any stage after conception, up to and including whelping. Sometimes a dog will be positive for relaxin on the first test, but will be negative on a later test. This indicates that the pregnancy has been lost, even though the dog may not have shown any sign of a problem.

Are there other ways of detecting pregnancy in the dog?

The traditional method of detecting pregnancy in the dog is careful abdominal palpation (gently pressing on the surface of the abdomen with the fingers) to detect swellings in the uterus that signal the presence of developing puppies. This method depends on the temperament, size, and body condition of the dog, as well as the timing of the palpation (the optimal time is between three and a half and five weeks of pregnancy), the number of fetuses present, and the experience of the person doing the palpation. Palpation is unreliable for determining the viability of the fetuses.dog_us

Abdominal radiographs (X-rays) are useful in detecting a pregnancy in the last trimester of gestation (three weeks before whelping), when the bony structures of the puppies can be seen. The viability of the puppies usually can be determined, although there are situations when it could be difficult; for example, the sudden death of a full term puppy in the uterus would be difficult to detect on radiograph. Radiographs are the best way to determine the numbers of puppies in a litter.

The most reliable way of detecting and monitoring pregnancy is abdominal ultrasound. Developing embryos can be detected as early as three weeks post-breeding and the viability of the fetuses can be determined throughout the pregnancy. Ultrasound is the ‘gold standard’ for detecting pregnancy and assessing the viability of the fetuses.


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