The hormone human chorionic gonadotropin (hCG) is produced during pregnancy and can be found in a pregnant woman's urine and blood; it indicates the presence of a fertilized egg. An earlier test, known as the AZ test, was developed by Selmar Aschheim and Bernhard Zondek. When urine from a woman in the early months of pregnancy was injected into immature female mice, their ovaries would enlarge and show follicular maturation. The test was considered reliable, with an error rate of less than 2%. Friedman and Lapham's test was essentially identical, but replaced the mouse with a rabbit. A few days after the injection, the animal would be dissected and the size of her ovaries examined.
The rabbit test became a widely used bioassay (animal-based test) to test for pregnancy. The term "rabbit test" was first recorded in 1949, and was the origin of a common euphemism, "the rabbit died," for a positive pregnancy test. The phrase was, in fact, based on a common misconception about the test. While many people assumed that the injected rabbit would die only if the woman was pregnant, in fact all rabbits used for the test died, as they had to be surgically opened in order to examine the ovaries.
A later alternative to the rabbit test, known as the "Hogben test," used the African clawed frog, and yielded results without the need to cut the animal open. Modern pregnancy tests continue to operate on the basis of testing for the presence of the hormone hCG in the blood or urine, but no longer require the use of a live animal.
- Rabbit Test, a 1978 film directed by Joan Rivers, starring Billy Crystal as the world's first pregnant man.
- "The assay of gonadotropic extracts in the post-partum rabbit". Journal of Endocrinology. 24 (5). May 1, 1939.
- Morris Fishbein, M.D., ed. (1976). "Aschheim-Zondek Test". The New Illustrated Medical and Health Encyclopedia. 1 (Home Library ed.). New York, N.Y. 10016: H. S. Stuttman Co. p. 139.
- Evans, Herbert M.; Simpson, Miriam E. (1930). "Aschheim-Zondek test for pregnancy - its present status". Calif West Med. 32 (3): 145–8. PMC . PMID 18741327.
- Wilton, Dave (28 February 2007). "rabbit test / the rabbit died". www.wordorigins.org. Retrieved 2018-07-30.
- Howe, Marvine (1991-03-10). "Dr Maurice Friedman 87 Dies Created Rabbit Pregnancy Test". The New York Times.
- Yong, Ed (2017-05-04). "How a Frog Became the First Mainstream Pregnancy Test". The Atlantic. Retrieved 2018-07-30.