There are several methods of diagnosing pregnancy in cats and dogs (and other pet species) but our preferred method is with ultrasound as this is the most reliable method.
Abdominal palpation: it may be possible to feel the pups/kittens in the abdomen after day 30 of pregnancy but this is a very unreliable method especially in animals with large abdomens. Pregnancy diagnosed by this method should always be confirmed by another method.
Relaxin blood test: This test is useful for early detection of pregnancy at day 21-28 but can be unreliable in that it sometimes gives a negative result when the animal is actually pregnant. A negative result should be confirmed by another test.
Abdominal ultrasound : This is our preferred method. Pregnancy can be detected as early as 21 days of pregnancy but it is much more accurate to perform the ultrasound examination at day 28-30. Ultrasound cannot be used to accurately count the number of foetuses. The only way to determine an accurate count is with an x-ray
Abdominal x-ray: The puppy or kitten skeleton does not become calcified until late in pregnancy so diagnosis of pregnancy with an x-ray can only be done after about day 45-50. For an accurate count of the number of foetuses you need to wait until day 55. An abdominal x-ray is the only reliable method of counting the number of foetuses.