Doctors Used to Use Live African Frogs As Pregnancy Tests

Pregnancy tests did not always come in an easy-to-use, sterile kit that provided almost immediate results. Less than a century ago, women had to rely upon frogs instead. In 1938, Dr. Edward R. Elkan wrote in the British Medical Journal:

The discovery of what is now known as the xenopus pregnancy test is based on experiments conducted by Hogben (1930, 1931), who observed that hypophysectomy produced ovarian retrogression, and the injection of anterior pituitary extracts ovulation, in the female South African clawed toad.

The African clawed frog, as its better known today, was imported around the world for its use in pregnancy tests. Doctors would ship urine samples to frog labs, where technicians would inject female frogs with a bit of the urine into their hind leg. The animals would be placed back into their tanks, and in the morning the technicians would check for tell-tale frog eggs dotting the water. If the female frog had ovulated, that meant the woman who provided the urine was pregnant and the pregnancy hormone, human chorionic gonadotropin, had kicked off ovulation in the frog. Researchers referred to this procedure as the Hogben test.

Among the 295 tests which I have done so far and in which 2,112 frogs were used I have not seen one clear positive that did not indicate a pregnancy. There were a few negative results which when repeated after a fortnight became positive, but I do not think that these can be regarded as failures.

Frogs were actually a great improvement on the previous means of testing whether or not a woman was pregnant. Welcome History describes:

Prior to Xenopus, female mice and rabbits had been used, but these had to be slaughtered, dissected and carefully examined for ovarian changes. Because toads were reusable and could be conveniently kept in aquaria, Xenopus made pregnancy testing practical on a larger scale than before.

Thousands of the frogs were exported across the world from the 1930s to 1950s for use as pregnancy testers.

Immunological test kits finally replaced Xenopus in the 1960s and were rapidly taken up by private companies and feminist organisations offering diagnostic services directly to women. The first over-the-counter home test was sold in pharmacies in the early 1970s, but it resembled a small chemistry set and so was not user-friendly. It was not until 1988 that the first recognisably ‘modern’ one-step-stick hit the shelves.

But the frogs’ legacy lives on. African clawed frogs can be found living around many urban centers today, where they were likely released into the wild after hospitals no longer had use for them. Additionally, the imported frogs are common pets, and no doubt some of those pets wear out their welcome and get chucked into a local stream or pond.

In 2006, researchers realized that the frog may be carriers for the deadly amphibian chytrid fungus, which has caused the extinction and decline of around 200 amphibian species around the world. Now, research published in PLoS One shows for the first time that populations of African clawed frogs living in California carry the fungus. The frogs can carry the disease for long periods without being affected themselves, so researchers suspect that they may be the original vectors that introduced the fungus around the world—a sort of revenge for being used as egg-laying research subjects for all those years.

More from Smithsonian.com:

Three New Frog Species Face an Uncertain Future
Crayfish Have Been Secretly Spreading a Deadly Frog Epidemic

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.