How Frogs Were Once Used to Detect Pregnancy

In a fruitful TED-Ed lesson written by Carly Anne York, PhD and animated by Yajun Shi, narrator Alexandra Panzer explains how the female African clawed frog (Xenopus laevis) was once used to detect pregnancy in humans due to her ability to constantly generate eggs. And, unlike the rabbits that were used previously, the frogs were not dissected afterwards.

They responded to hCG in roughly 9 hours with no need for dissection. And since their large ovaries constantly generate eggs, they could participate in numerous tests over their 15 to 30 year lifespan. Better still, these frogs were abundant in their native habitat, making them easy to find, catch, and export.

This led to the presence of these frogs in hospitals around the world. Unfortunately, this led to unintended but unsurprising side effects.

More than a few of these amphibians have escaped their laboratory enclosures, and in many places, their ferocious appetite allowed them to outcompete native amphibians.…they often carry a deadly fungus called chytrid, which can cause an infection that lethally disrupts the delicate functioning of amphibian skin. In the 20th century, this fungal infection has devastated amphibian populations around the globe, causing the extinction of multiple frog species.

This practice lasted until the 1970s, after which time doctors had access to chemically-derived tests that could detect the presence of hCG indicating pregnancy. And the use of African clawed frogs became illegal and their presence is now considered invasive.

…the African clawed frog is now classified as an invasive species, and illegal in many regions. So in the end, like other pregnancy tests, the use of these frogs in scientific research has had both positive and negative results.