Pregnancy Diagnosis in the Dog

Until recently pregnancy diagnosis in the dog depended on abdominal palpation (i.e. feeling for foetuses through the abdominal wall), radiography (x-ray) or an ultrasound scan.

However, it is now possible to accurately detect pregnancy in the dog with a simple blood test.

How does it work?

The test detects the presence of relaxin in the blood sample. Relaxin is a hormone which is produced by the developing placenta in the womb and can be detected in the blood of most dogs as early as 22-27 days after mating. Relaxin levels remain elevated throughout pregnancy but decline rapidly following separation of the placenta at parturition.

Will this test differentiate between pregnancy and pseudo pregnancy (phantom pregnancy)?

In some dogs a false pregnancy can be extremely difficult to differentiate from true pregnancy. However, during pseudo pregnancy there is no placental development and therefore no relaxin is produced. Hence the blood test will be negative and it can be reliably assumed that the dog, who may be exhibiting all the signs of pregnancy, including lactation, bed making etc is not pregnant.

Is the test sufficiently reliable that I can assume a negative result really does mean that my dog is not pregnant?

The test depends upon measuring circulating blood levels of relaxin produced by the placenta. If the test is performed very early in pregnancy, before the placenta is sufficiently developed, the level of circulating relaxin may be too low to be detected. Thus if the dog is tested between the third and fourth week of mating, it is worthwhile repeating the test again a week later. Similarly if accurate mating dates are unknown and the result is negative, repeat testing is worthwhile.

Do false positives occur?  In other words can I rely on a positive blood test that my dog is pregnant?

A positive result for the relaxin blood test indicates that a placenta was present when the blood sample was taken. However, this does not preclude the possibility that the dog may abort the foetuses particularly if the test was performed early in the pregnancy, ie. 22-27 days post mating. Occasionally a dog tested more than once will be positive on the first test and negative later on. This indicates that the pregnancy has been lost even though the dog may not have given any indication that anything was wrong.

Are there any other methods by which pregnancy can be detected earlier than 3-4 weeks?

• Transabdominal palpation will sometimes detect pregnancy just before three weeks but this depends upon a lean, cooperative dog and a skilled, experienced person doing the palpation.
• An ultrasound scan, again in the hands of an experienced operator, can sometimes indicate pregnancy as early as 16-21 days and can give information about the viability and age of the foetuses.