Early pregnancy tests used... frogs?

Forgive me, this is well known research, and I link to an old article in Slate, but I only just learned this fact today.

In the 1930s, scientists used frogs to help determine if a woman was pregnant or not, according to this article. How? You ask. Well...

You inject some urine into its dorsal lymph sac in the morning and check back at the end of the day. A dose of a pregnant woman's pee will cause a female South African clawed frog to lay eggs within eight to 12 hours. The test also works on male frogs, which produce sperm in response to the injection.

Frogs were used because their ovulation is easily controlled. And, the test worked because of a hormone called human chorionic gonadotropin or hcg. Modern tests use hcg as well, it contains antibodies that react to the hcg.

And, I bet the whole thing is a fact you never knew.