The “rabbit test” was a historical biological assay used to detect pregnancy. This test involved injecting a woman’s urine into a female rabbit and observing the animal’s physiological response. It was an important early method for confirming pregnancy before modern, animal-free techniques existed.
How the Test Was Performed
The procedure for the rabbit test, also known as the Friedman test, began with collecting a woman’s urine sample. This sample was then injected into a virgin female rabbit, often intravenously into an ear vein.
After the injection, a waiting period of about 48 hours was observed. The rabbit was then euthanized, and its abdomen surgically opened for examination. The key step involved inspecting the rabbit’s ovaries for specific changes indicative of pregnancy. The rabbit was always killed for this examination, regardless of the test result.
The Biological Basis
The scientific principle behind the rabbit test relied on human chorionic gonadotropin (hCG), a hormone produced during pregnancy. After a fertilized egg implants, the developing placenta secretes hCG, which appears in the pregnant woman’s urine. When urine containing hCG was injected into a female rabbit, the hormone stimulated the rabbit’s ovaries.
This stimulation caused observable changes in the ovaries, such as enlargement and the development of hemorrhagic follicles or corpora lutea. These ovarian reactions indicated pregnancy. If the rabbit’s ovaries showed these changes, it meant hCG was present in the urine, confirming pregnancy.
Its Place in Medical History
The rabbit test emerged from earlier work by Selmar Aschheim and Bernhard Zondek in 1928, who developed a similar test using mice. Maurice Friedman and Maxwell Lapham adapted this method in 1931, substituting mice with rabbits, creating the Friedman test or “rabbit test.” This biological assay offered one of the first reliable and accurate methods for pregnancy detection.
The test’s use led to the common euphemism, “the rabbit died,” to signify a positive pregnancy. Despite its reported effectiveness of up to 98%, the test was eventually phased out. Using live animals and requiring dissection raised ethical concerns and made the test time-consuming and expensive. Modern immunoassay-based tests developed in the 1960s detect hCG without animals, offering faster, more convenient results, leading to the obsolescence of the rabbit test and similar bioassays.