There are, and you can apparently get them off of Amazon. But I'm assuming that they aren't very accurate and by the time they are you're bringing the dog in for an xray headcount anyways.
I also want pregnancy test for doggies! I have tried humans pregnancy test to one of our dog and guess what, it didn't work lol. But the rumors what that little test caused in this small town where worth of buying that test just for a dog .
Because dogs are weird, hormonally speaking, and none of the hormone-based stuff is accurate at all. For example, in most other mammals estrogen increases and progesterone decreases right before ovulation. In dogs, it is the opposite. Also, the progesterone levels continue to rise and then plateau regardless whether the bitch gets pregnant. What's more, dogs very commonly have false pregnancies, which a hormone test would not be able to detect. Ultrasound is the only reliable way for early detection. (X-ray is more reliable, but necessitates later use because it can harm developing fetuses.)
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EDIT: Some of them can also be quite expensive: http://www.tscpets.com/13973.html?productid=13973&channelid=FROOG