The earliest written record of urine-based pregnancy tests comes from over 3000 years ago by Egyptians. They were tests based on the germination of seeds and the rate of plant growth after being given urine. Interestingly, it has been proven that pregnancy urine does have a beneficial effect on plant growth due to the human chorionic gonadotropin (hCG) hormone [1,2].
In the 20th century, it became common to test human pregnancy on other animals. The Schheim-Zondek Test (1927), Frank Rat Test (1933), Friedman Test (1929), and Toad-Hogben Tests (1934-1940) were conducted by injecting human urine on immature mice, rats, rabbits, and toads respectively [2]. If the urine contained hCG (a.k.a there was a pregnancy), the animals would have changes in their ovaries or, in the case of toads, release spermatozoa. Since these tests were based on animal subjects, they were expensive, time consuming, easily false-positive or false-negative, and resulted in the sacrifice of many animals.
By 1950, pregnancy testing had progressed to detect the presence of hCG in human urine directly. However, these tests had several drawbacks, the two main ones being the inability to detect early pregnancy and differentiate between hCG and Luteinizing hormone (LH) levels [3, 4]. More information about the different hormones in the menstrual cycle here.
As tests were so inaccurate and expensive, the thermometer was the only home diagnostic tool [5]. This is because basal temperature increases and decreases following the menstrual cycle. When pregnant, the temperature will increase at ovulation and stay elevated. Therefore, a rise in body temperature for more than 18 days could be an early indicator of pregnancy [6].
The first home pregnancy kit was introduced in 1976 [1]. The “error proof test” (e.p.t) by Warner-Chilcott was only $10 and included a vial of purified water, a test tube with sheep red blood cells, and a medicine dropper [7]. The sheep red blood cells would interact with the hCG contents in the urine. If there is hCG, the blood stayed normal, however, if there is a lack of, the blood would clump up [8]. When used correctly, it took 2 hours and provided a 97% accuracy [1].
The accuracy and quality of the test has been improved over time with faster and more reliable ones. Currently, modern pregnancy tests use immunohistochemistry to detect hCG in urine at very early stages of pregnancy [3, 5, 9]. If you are interested in knowing about how current pregnancy tests work, stay tuned for next week’s post!
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Written by: Phaedra
Edited by: María and Natasha
BioDecoded is a volunteer group committed to sharing accurate scientific information. If you have any questions about this topic or would like to learn more, please comment below or send us your questions.
References:
Leavitt S. (2006). A private little revolution: the home pregnancy test in American culture. Bull Hist Med 80:317–45. Available at: https://pubmed.ncbi.nlm.nih.gov/16809866/
Ferreira HP. (1954). The relative merits of the various biological tests for pregnancy. Postgrad Med Journal P355-359. Available at: https://pubmed.ncbi.nlm.nih.gov/13177232/
Jones RJ and Lopez KH (2014). Pregnancy. Human Reproductive Biology, 4th (10). p 175-204. Available at: https://shop.elsevier.com/books/human-reproductive-biology/jones/978-0-12-382184-3
Pregnancy Test Timeline - Office of NIH History and Stetten Museum (2023). Available at: https://history.nih.gov/display/history/Pregnancy+Test+Timeline (Accessed: 5 February 2023).
Plebani M (2021). Home pregnancy tests: quality first. Clin Chem Lab Med 59(5): 795–796. Available at: https://www.degruyter.com/document/doi/10.1515/cclm-2020-1797/html
Basal body temperature for natural family planning - Mayo Clinic (2023). Available at: https://www.mayoclinic.org/tests-procedures/basal-body-temperature/about/pac-20393026# (Accessed: 5 February 2023).
Magazine, S. and Blakemore, E. (2015). This is What the First Home Pregnancy Test Looked Like - Smithsonian Magazine. Available at: https://www.smithsonianmag.com/smart-news/what-first-home-pregnancy-test-looked-180955478/ (Accessed: 5 February 2023).
Pee is for Pregnant: The history and science of urine-based pregnancy tests - Science in the News (2018). Available at: https://sitn.hms.harvard.edu/flash/2018/pee-pregnant-history-science-urine-based-pregnancy-tests/ (Accessed: 5 February 2023).
Gnoth C. Johnson S. (2014). Strips of Hope: The accuracy of home pregnancy tests and new developments. Geburtshlife und Frauenheilkunde 74(7): 661-669. Available at: https://pubmed.ncbi.nlm.nih.gov/25100881/
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