The rabbit test. A womans urine was injected into a rabbit. The lab would then check the rabbits ovaries for a certain chemical that would effect the ovaries only if the woman was pregnant.
Before blood tests & home pregnancy tests, how did a woman know if she was pregnant or not?
I would have to say after years and years, women got wise to the fact that if they didn't have their periods, they'd soon be squeezing out a watermelon! That coupled with their growing belly....I think it was probably a learning thing, ya know, you only put your finger to the flame so many times before you realize it's hot!