Partridge's Concise Dictionary of slang gives the original phrase as "dog's ballocks", but that's just a variant selling of "bollocks" so it doesn't help us much.

The full entry in Partridge is: "dog's ballocks. The typographical colon-dash (:-). See dog's prick. - 2. Esp. in the phrase 'it sticks out like a dog's ballocks', said of something that the speaker considers patently obvious: low, since ca 1920."

Dog's prick, incidentally, is given the same definition Dr Price gives it above: an exclamation mark.

Cassell's Dictionary of Slang agrees with Partridge as far as the 1920s usage is concerned, adding that the meaning of "dog's bollocks" as "excellent" seems to date from the 1980s.

My guess is that the switch in meaning occurred when someone noticed that both "dog's bollocks" and "bee's knees" were descriptions of a creature's body parts - a similarity that's accentuated by the fact that both phrases are plural - and started using one term in the sense of the other. "Dog's bollocks" has an appealing crudity about it which may have helped it to catch on.

What I want to know, though, is why "up the stick" became a slang term to describe pregnancy. What stick, precisely? And why is ascending it deemed relevant in this context?