By D. Caroline Coile, Ph.D.
You’ve bred your bitch. But how do you know if it’s time to start work on the nursery? There are plenty of clues and tests you can use.
But first, why can’t she just take a human pregnancy test? The reason is that human tests detect the presence of human chorionic gonadatropin (HCG), which dogs don’t produce. One problem with using other hormone tests for bitches is that both pregnant and non-pregnant bitches experience increased progesterone levels following estrus – the phenomenon responsible for false pregnancies. Although progesterone is higher in pregnant than in non-pregnant bitches, there’s enough overlap to make testing meaningless.
Hormone testing
Pregnant bitches do, however, produce one hormone that non-pregnant bitches don’t: relaxin. This hormone is produced when the fertilized egg is implanted, and remains in the blood throughout pregnancy. It can take about 21 to 25 days following fertilization for the egg to implant and produce detectable levels of relaxin in the blood, so for best results, wait about 28 days post-breeding to perform the test.
It’s possible to be overanxious and check for relaxin too soon, but if you test too early the results will indicate your bitch isn’t pregnant. If this happens, a subsequent test the next week will give more accurate results.
A positive result might mean that a litter was conceived and then lost; relaxin levels would still be high and indicate she was pregnant even though no puppies remain. So although the test is simple, requiring only blood work, it’s only accurate after a time when other tests could be used, and can’t give you any idea of litter size.
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