A pregnancy test that asked a frog to lay eggs
In the 1950s, some hospitals tested urine by injecting a sample into a female African clawed frog, Xenopus laevis. If the patient was pregnant, the frog could begin laying eggs within hours. The eggs—not a change in the frog’s appearance—were the test’s visible result.
The hormone that triggered the response
Pregnancy causes the body to produce human chorionic gonadotropin, or hCG, which passes into urine. In the frog, that hormone stimulated the ovaries to release eggs. The test worked because the animal’s reproductive system responded to a human hormone strongly enough to produce a clear, observable result.
Why hospitals used a living animal
Before modern test kits, detecting pregnancy meant looking for biological effects rather than reading a chemical strip. The frog test was useful because it was relatively quick and, unlike an earlier rabbit test, did not require killing the animal to determine the result. A frog that laid eggs could be kept and used again after a recovery period.
The oddness was also the method’s practical strength: instead of trying to see a tiny hormonal change directly, the test turned it into something unmistakable—a cluster of eggs in a container.
