African clawed frogs

(Xenopus laevis) played a surprising but important role in human medicine—specifically in pregnancy testing—from the 1930s through the 1960s.

The Pregnancy Test Method

In the early 20th century, scientists discovered that the urine of pregnant women contains the hormone human chorionic gonadotropin (hCG).

Researchers found that when urine from a pregnant woman was injected into a female African clawed frog, the frog would respond by laying eggs within about 12 hours, even outside of its normal breeding season.

This became known as the “frog test” (sometimes called the “Hogben test” after British zoologist Lancelot Hogben, who pioneered the technique in 1930).

Why African Clawed Frogs?

They were hardy, easy to care for, and could survive in laboratory conditions.

Their reproductive system responded reliably and visibly to hCG.

Unlike earlier animal-based tests that used rabbits or mice (which had to be killed to examine ovarian changes), the frogs could be reused many times.

Impact on Medicine

The frog test was considered the first reliable and relatively humane pregnancy test.

It became widely used around the world until laboratory-based immunoassay tests for hCG were developed in the 1960s and 70s, which were faster and didn’t require live animals.

Interestingly, the widespread global trade of African clawed frogs for medical use is thought to have contributed to the spread of the deadly amphibian fungal disease chytridiomycosis.