“The Rabbit Died”: The Evolution of the Pregnancy Test

You hear the phrase in in old movies: Someone gets told “the rabbit died” and everyone understands that to mean they are pregnant.

But what does the death of a rabbit have to do with a human pregnancy?

The rabbit test, also known as the Friedman test, was one of the first early accurate tests for pregnancy. It was a bioassay test in which a small sample of a woman’s urine was injected into a female rabbit several times over the course of a few days.

In a pregnant woman, a hormone called human chorionic gonadotropin (hCG) is present. The hCG in the injection would cause the rabbit’s ovaries to enlarge. To find out if the ovaries were enlarged, the rabbit was killed and dissected. So, saying “The rabbit died,” as a slang way to announce pregnancy is wrong, since the rabbit involved in the test always died whether someone was pregnant or not.

hCG is produced in a human body during pregnancy, starting after an egg has been fertilized. It can be found in both urine and blood. Before the discovery of hCG, a woman might suspect she was pregnant by  physical signs such as morning sickness and weight gain.

The only way for a woman to know for sure that she was pregnant was when she felt the baby start kicking, an event known as quickening. Even that could be missed, and some joked that the only sure proof of a pregnancy was labor and delivery.

But there have always been methods to test for a pregnancy. The only problem was that few of them worked well, if at all. Curiously, many involved urine.

The ancient Egyptians had a test for pregnancy that involved urine. A woman who thought she was pregnant would put a combination of wheat and barley seeds on the ground and pee on it for several days. If the seeds started to grow, she was pregnant. The test actually went further and was also thought to predict the sex of the baby. If the barley grew, the baby was a boy. If the wheat grew, the baby was a girl. It might actually have had some basis in fact since a pregnant woman’s urine contains high amounts of estrogen, which could have caused the seeds to grow.

In the middle ages, there were physicians who said they could diagnose many conditions, including pregnancy, by examining a sample of urine for its color and smell. Some doctors mixed wine into a sample of a woman’s urine to see if certain reactions happened.

Accuracy in pregnancy tests didn’t arrive until the twentieth century. The rabbit test was developed in 1931 by Maurice Friedman and Maxwell Edward Lapham, who were reproductive physiology researchers. It was an advancement over the AZ test, developed by Selmar Aschheim and Bernhard Zondek, two European researchers who discovered hCG. Their test, developed in 1927 and known as the AZ test, injections of a small amount of urine into immature female mice. As with the rabbit test, all the mice were killed and dissected to see if their ovaries had reacted to hCG.

The AZ test and the rabbit test fell out of favor when a better test came along that did not involve small mammals. The Hogben test used frogs instead, specifically the female African clawed frog, and again involved injecting urine into the frog. However, it didn’t involve killing the frogs. If the urine contained hCG, the frog would lay eggs within a day. The same frog could be used again and again.

One of the downsides to these tests, in addition to the death of countless mice and rabbits, was that they took time and were expensive. All three tests took several days at the very least to produce an answer. Because of the cost, only the well-off could afford the tests. The tests were also not particularly accurate, since they depended on relatively high levels of hCG to be present in the urine.

The rabbit test was used until the 1970s when accurate and faster tests for HCG became available. These tests were done in laboratories or doctor’s offices and took a few hours to produce an answer. Even so, pregnancy testing was not performed regularly. Most women only went to the doctor when they were showing all the common physical symptoms of a pregnancies like the lack of periods and weight gain.

In 1976, the first rapid tests for pregnancy became available over-the-counter were approved, which meant that women could find out if they were pregnant in the privacy of their own homes. These tests reached the market in 1978. Originally, they took two hours to show results and involved the use of a little chemistry set that included an eye dropper and test tubes. Now home pregnancy tests are a plastic wand that you urinate on, and which can give a result in about 15 minutes. Millions are sold and used each year.

Valerie DeBenedette
Valerie DeBenedette is an experienced health and medical writer who lives about an hour north of New York City with a dog that is smaller than her cat. Her work has appeared in magazines, newspapers, newsletters, and on websites. She is a member of the National Association of Science Writers.

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