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The current pregnancy tests are simple and fast, you have to urinate on a plastic wand and wait a few minutes for the essential hormone of pregnancy to be detected: Human Chorionic Gonadotropin.

But during the 1920s tests to detect this hormone were much slower and less assertive. How, then, could women make sure they were pregnant or not?

There was the so-called Aschheim-Zondek test, or "A-Z" test consisted of detecting the presence of chorionic gonadotropin (HCG). The woman's urine was injected to rodents that were exterminated to then examine their ovaries and detect pregnancy hormones.

But there was another test that was also discovered at that time and that worked for more than two decades, the "Hogben" test. It began in 1930 when the English biologist Lancelot Hogben began researching the African nail frog, also called Xenopus laevis.

While teaching in South Africa, Hogben learned that these frogs were sensitive to hormonal changes and noticed that injecting these animals with the hypophyseal extract of another frog could encourage their ovulation in a matter of hours, according to a study published in the International Journal of Developmental Biology

Based on Hogben's research, other scientists found that these frogs could serve as a simple pregnancy test. In 1937 Hobgben and the animal geneticist Francis Albert Eley Crew imported some 1500 Xenopus frogs to England and they knew how to raise them for pregnancy tests within two years.

"We took a woman's urine and injected it into the frog, if the frog gave eggs after 12 to 24 hours had elapsed, you knew that the woman was pregnant," said Marko Hobo, researcher at the National Xenopus Resource, at the site. Business Insider

He added that this method with frogs was basically the predecessor of home pregnancy tests. But in that it was not so simple that women had access to the "Hogben" test, they had to go to a doctor to give them a laboratory recipe. The typical current pregnancy test came in the 1960s.

Although eventually this type of test ceased to exist the work of Hogben and other scientists to Xenopus frogs served as an experiment for many scientific tests, both in Europe and the United States.

Horb says scientists use frogs to study everything from biology to heart disease and are even using them to study kidney disease.