A pregnancy test detects human pregnancy hormone (human chorionic gonadotropin (hCG)) to determine whether an individual is pregnant.
HCG testing can be performed on a blood sample (typically done in a medical office or hospital) or on urine (which can be performed in an office, hospital or at home.)
The most common tests use markers found in blood and urine, specifically one called human chorionic gonadotropin (hCG). Identified in the early 20th century, hCG rises quickly in the first few weeks of pregnancy, peaking at 10 weeks. It is produced by the syncytiotrophoblast cells of the fertilised ova (eggs) as the cells invade the uterus' lining and start forming what will become placenta.
Urine tests will typically show positive around four weeks after the last menstrual period (LMP) and are best done in the morning as hCG levels are then highest. Because of their cut-off hCG level, a positive result is less likely to be incorrect than a negative one, and how much water/fluids have been consumed can affect the results as well. Blood hCG tests for a more specific part of the hCG molecule and can detect pregnancy earlier than urine, even before a period has been missed. Obstetric ultrasonography may also be used to detect pregnancy. The order of detection from earliest to latest is that hCG can be detected earliest in the blood, then a urine test, then ultrasound.
Chemical tests for pregnancy look for the presence of the beta subunit of human chorionic gonadotropin (hCG) in the blood or urine. For a qualitative test (yes/no results only), the thresholds for a positive test are generally determined by an hCG cut-off where at least 95% of pregnant women would get a positive result on the day of their first missed period. hCG can be detected in urine or blood after implantation around six to twelve days after fertilization, although some evidence suggests that hCG may be released preimplantation as well. Quantitative blood (serum beta) tests can detect hCG levels as low as 1 mIU/mL, and typically clinicians will call a positive pregnancy test at 5mIU/mL. Urine test strips have published detection thresholds of 10 mIU/mL to 100 mIU/mL, depending on the brand. Most home pregnancy tests are based on lateral-flow technology.
With obstetric ultrasonography the gestational sac sometimes can be visualized as early as four and a half weeks of gestation (approximately two and a half weeks after ovulation) and the yolk sac at about five weeks' gestation. The embryo can be observed and measured by about five and a half weeks. The heartbeat may be seen as early as six weeks, and is usually visible by seven weeks' gestation.
Although all current pregnancy tests detect the presence of beta hCG, research has identified at least one other possible marker that may appear earlier and exclusively during pregnancy. For example, early pregnancy factor (EPF) can be detected in blood within 48 hours of fertilization, rather than after implantation. That said, its reliable use as a pregnancy test remains unclear as studies have shown its presence in physiological situations besides pregnancy, and its application to humans remains limited.
A systematic review published in 1998 showed that home pregnancy test kits, when used by experienced technicians, are almost as accurate as professional laboratory testing (97.4%). When used by consumers, however, the accuracy fell to 75%: the review authors noted that many users misunderstood or failed to follow the instructions included in the kits. Improper usage may cause both false negatives and false positives.
Timing of test
False negative readings can occur when testing is done too early. Quantitative blood tests and the most sensitive urine tests usually begin to detect hCG shortly after implantation, which can occur anywhere from 6 to 12 days after ovulation. hCG levels continue to rise through the first 20 weeks of pregnancy, so the chances of false negative test results diminish with time (gestation age). Less sensitive urine tests and qualitative blood tests may not detect pregnancy until three or four days after implantation. Menstruation occurs on average 14 days after ovulation, so the likelihood of a false negative is low once a menstrual period is late.
Ovulation may not occur at a predictable time in the menstrual cycle, however. A number of factors may cause an unexpectedly early or late ovulation, even for women with a history of regular menstrual cycles. Using ovulation predictor kits (OPKs), or charting the fertility signs of cervical mucus or basal body temperature give a more accurate idea of when to test than day-counting alone.[unreliable medical source?]
The accuracy of a pregnancy test is most closely related to the day of ovulation, not of the act of intercourse or insemination that caused the pregnancy. It is normal for sperm to live up to five days in the fallopian tubes, waiting for ovulation to occur.[unreliable medical source?] It could take up to 12 further days for implantation to occur, meaning even the most sensitive pregnancy tests may give false negatives up to 17 days after the act that caused the pregnancy. Because some home pregnancy tests have high hCG detection thresholds (up to 100 mIU/mL), it may take an additional three or four days for hCG to rise to levels detectable by these tests — meaning false negatives may occur up to three weeks after the act of intercourse or insemination that causes pregnancy.
False positive test results may occur for several reasons, including errors of test application, use of drugs containing the hCG molecule, and non-pregnant production of the hCG molecule. Urine tests can be falsely positive in those that are taking the medications: chlorpromazine, phenothiazines and methadone among others.
Spurious evaporation lines may appear on many home pregnancy tests if read after the suggested 3–5 minute window or reaction time, independent of an actual pregnancy. False positives may also appear on tests used past their expiration date.
A woman who has been given an hCG injection as part of infertility treatment will test positive on pregnancy tests that assay hCG, regardless of her actual pregnancy status. However, some infertility drugs (e.g., clomid) do not contain the hCG hormone.[medical citation needed]
Some diseases of the liver, cancers, and other medical conditions may produce elevated hCG and thus cause a false positive pregnancy test. These include choriocarcinoma and other germ cell tumors, IgA deficiencies, heterophile antibodies, enterocystoplasties, gestational trophoblastic diseases (GTD), and gestational trophoblastic neoplasms.
Pregnancy tests may be used to determine the viability of a pregnancy, defined as a whether a pregnancy has the potential to result in a live birth. Serial quantitative blood tests may be done, usually 48 hours apart, and interpreted based on the knowledge that hCG in a viable normal pregnancy rises in a curvilinear fashion. For example, for a starting hCG level of 1,500 mIU/ml or less, the hCG of viable pregnancy will increase at least 49% in 48 hours. However, for pregnancies with a higher starting hCG, between 1,500-3,000 mIU/ml, the hCG should rise at least 40%; for a starting hCG greater than 3,000 mIU/ml, the hCG should increase at least 33%. Failure to rise by these minimums indicates that the pregnancy is not viable, either as a failed intrauterine pregnancy or a possible ectopic pregnancy.
Ultrasound is also a common tool for determining viability of a pregnancy. Serial ultrasound may be used to identify non-viable pregnancies, as pregnancies that do not grow in size or develop expected structural findings on repeated ultrasounds over a 1-2 week interval may be identified as abnormal. Occasionally, a single ultrasound may be used to identify a pregnancy as non-viable; for example, an embryo that is greater than a certain size but that lacks a visible heart beat may be confidently determined to be not viable without the need for follow up ultrasound for confirmation.
Records of attempts at pregnancy testing have been found as far back as the ancient Greek and ancient Egyptian cultures. The ancient Egyptians watered bags of wheat and barley with the urine of a possibly pregnant woman. Germination indicated pregnancy. The type of grain that sprouted was taken as an indicator of the fetus's sex. Hippocrates suggested that a woman who had missed her period should drink a solution of honey in water at bedtime: resulting abdominal distention and cramps would indicate the presence of a pregnancy. Avicenna and many physicians after him in the Middle Ages performed uroscopy, a nonscientific method to evaluate urine.
Selmar Aschheim and Bernhard Zondek introduced testing based on the presence of human chorionic gonadotropin (hCG) in 1928. Early studies of hCG had concluded that it was produced by the pituitary gland. In the 1930s, Doctor Georgeanna Jones discovered that hCG was produced not by the pituitary gland, but by the placenta. This discovery was important in relying on hCG as an early marker of pregnancy. In the Aschheim and Zondek test, an infantile female mouse was injected subcutaneously with urine of the person to be tested, and the mouse later was killed and dissected. Presence of ovulation indicated that the urine contained hCG and meant that the person was pregnant. A similar test was developed using immature rabbits. Here, too, killing the animal to check her ovaries was necessary.
At the beginning of the 1930s, Hillel Shapiro and Harry Zwarenstein, who were researchers at the University of Cape Town, discovered that if urine from a pregnant female was injected into the South African Xenopus toad and the toad ovulated, this indicated that the woman was pregnant. This test was used throughout the world from the 1930s to 1960s, with Xenopus toads being exported live in great numbers. Shapiro's advisor, Lancelot Hogben, claimed to have developed the pregnancy test himself, but refuted by both Shapiro and Zwarenstein in a letter to the British Medical Journal. A later article, independently authored, granted Hogben credit for the principle of using Xenopus to determine gonadotropin levels in pregnant women's urine, but not for its usage as a functional pregnancy test.
Hormonal pregnancy tests such as Primodos and Duogynon were used in the 1960s and 1970s in the UK and Germany. These tests involved taking a dosed amount of hormones, and observing the response a few days later. A pregnant woman does not react, as she is producing the hormones in pregnancy; a woman not pregnant responds to the absence of the hormone by beginning a new menstrual cycle. While the test was (is) generally considered accurate, research advancements have replaced it with simpler techniques.
Immunologic pregnancy tests were introduced in 1960 when Wide and Gemzell presented a test based on in-vitro hemagglutination inhibition. This was a first step away from in-vivo pregnancy testing and initiated a series of improvements in pregnancy testing leading to the contemporary at-home testing. Direct measurement of antigens, such as hCG, was made possible after the invention of the radioimmunoassay in 1959. Radioimmunoassays require sophisticated apparatus and special radiation precautions and are expensive.
Organon International obtained the first patent on a home pregnancy test in 1969, two years after product designer Margaret Crane noticed that the laboratory testing procedure was relatively simple and made a prototype. The product became available in Canada in 1971, and the United States in 1977, after delays caused by concerns over sexual morality and the ability of women to perform test and cope with the results without a doctor.
Another home pregnancy testing kit was based on the work of Judith Vaitukaitis and Glenn Braunstein, who developed a sensitive hCG assay at the National Institutes of Health. That test went onto the market in 1978. In the 1970s, the discovery of monoclonal antibodies led to the development of the relatively simple and cheap immunoassays, such as agglutination-inhibition-based assays and sandwich ELISA, used in modern home pregnancy tests. Tests are now so cheap that they can be mass-produced in a general publication and used for advertising.
- Cole, Laurence A (2010). "Biological functions of hCG and hCG-related molecules". Reproductive Biology and Endocrinology. 8 (1): 102. doi:10.1186/1477-7827-8-102. ISSN 1477-7827. PMC 2936313. PMID 20735820.
- Medical physiology : principles for clinical medicine. Rhoades, Rodney., Bell, David R., 1952- (3rd ed.). Philadelphia: Lippincott Williams & Wilkins. 2009. ISBN 9780781768528. OCLC 144771424.CS1 maint: others (link)
- Casanova, Robert; Weiss, Patrice M. (April 2018). Beckmann and Ling's obstetrics and gynecology. Casanova, Robert,, Chuang, Alice,, Goepfert, Alice R.,, Hueppchen, Nancy A.,, Weiss, Patrice M.,, American College of Obstetricians and Gynecologists (8th ed.). Philadelphia. ISBN 9781496353092. OCLC 949870151.
- Handbook of clinical laboratory testing during pregnancy. Gronowski, Ann M. Totowa, N.J.: Humana Press. 2004. ISBN 1588292703. OCLC 53325293.CS1 maint: others (link)
- Wilcox AJ, Baird DD, Weinberg CR (1999). "Time of implantation of the conceptus and loss of pregnancy". New England Journal of Medicine. 340 (23): 1796–1799. doi:10.1056/NEJM199906103402304. PMID 10362823.
- Waddell, Rebecca Smith (2006). "FertilityPlus.org". Home Pregnancy Test hCG Levels and FAQ. Archived from the original on 2006-06-15. Retrieved 2006-06-17.
- Woo, Joseph (2006). "Why and when is Ultrasound used in Pregnancy?". Obstetric Ultrasound: A Comprehensive Guide. Retrieved 2007-05-27.
- Boschert, Sherry (15 June 2001). "Anxious Patients Often Want Very Early Ultrasound Exam". OB/GYN News. FindArticles.com. Retrieved 2007-05-27.
- Fan XG, Zheng ZQ (1997). "A study of early pregnancy factor activity in preimplantation". Am. J. Reprod. Immunol. 37 (5): 359–64. doi:10.1111/j.1600-0897.1997.tb00244.x. PMID 9196793.
- Clarke FM. Controversies in assisted reproduction and genetics. Does "EPF" have an identity?. J Assist Reprod Genet. 1997;14(9):489–491. doi:10.1023/a:1021110906666
- Bastian LA, Nanda K, Hasselblad V, Simel DL (1998). "Diagnostic efficiency of home pregnancy test kits. A meta-analysis". Arch Fam Med. 7 (5): 465–9. doi:10.1001/archfami.7.5.465. PMID 9755740. Archived from the original on 2008-12-06. Retrieved 2008-05-12.
- Wilcox AJ, Baird DD, Weinberg CR (June 1999). "Time of implantation of the conceptus and loss of pregnancy". New England Journal of Medicine. 340 (23): 1796–9. doi:10.1056/NEJM199906103402304. PMID 10362823.
- Weschler, Toni (2002). Taking Charge of Your Fertility (Revised ed.). New York: HarperCollins. pp. 374. ISBN 0-06-093764-5.
- Ellington, Joanna (2004). "Sperm Transport to the Fallopian Tubes". Frequently Asked Questions with Dr. E. INGfertility Inc. Archived from the original on 2006-07-13. Retrieved 2006-08-13.
- Wallach, Jacques (2007). Interpretation of diagnostic tests (8th ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. p. 866. ISBN 9780781730556.
- Stenman, Ulf-Håkan; Alfthan, Henrik; Hotakainen, Kristina (July 2004). "Human chorionic gonadotropin in cancer". Clinical Biochemistry. 37 (7): 549–561. doi:10.1016/j.clinbiochem.2004.05.008. PMID 15234236.
- "ACOG Practice Bulletin No. 193: Tubal Ectopic Pregnancy". Obstetrics & Gynecology. 131 (3): e91–e103. March 2018. doi:10.1097/AOG.0000000000002560. ISSN 0029-7844.
- Doubilet, Peter M.; Benson, Carol B.; Bourne, Tom; Blaivas, Michael (2013-10-10). Campion, Edward W. (ed.). "Diagnostic Criteria for Nonviable Pregnancy Early in the First Trimester". New England Journal of Medicine. 369 (15): 1443–1451. doi:10.1056/NEJMra1302417. ISSN 0028-4793.
- Clark, Stephanie Brown. (2005).Jan Steen: The Doctor's Visit.Literature, Arts, and Medicine Database. Retrieved 27 May 2007.
Lubsen-Brandsma, M.A. (1997). Jan Steen's fire pot; pregnancy test or gynecological therapeutic method in the 17th century?. Ned Tijdschr Geneeskd, 141(51), 2513–7. Retrieved 24 May 2006.
"The Doctor's Visit." (n.d.). The Web Gallery of Art. Retrieved 24 May 2006.
- Speert, Harold (1973). Iconographia Gyniatrica. Philadelphia: F. A. Davis. ISBN 978-0-8036-8070-8.
- Damewood MD, Rock JA (August 2005). "In memoriam: Georgeanna Seegar Jones, M.D.: her legacy lives on" (PDF). Fertility and Sterility. American Society for Reproductive Medicine. 84 (2): 541–2. doi:10.1016/j.fertnstert.2005.04.019. PMID 16363033. Archived from the original (PDF) on 2008-12-09. Retrieved 2007-12-31.
- Christophers, S. R. (1946-11-16). "The Government Lymph Establishment". Br Med J. 2 (4480): 752. doi:10.1136/bmj.2.4480.752. ISSN 0007-1447. PMC 2054716.
- SHAPIRO, H. A.; ZWARENSTEIN, H. (1934-05-19). "A Rapid Test for Pregnancy on Xenopus lævis". Nature. 133 (3368): 762. doi:10.1038/133762a0. ISSN 0028-0836.
- Gurdon, J B; Hopwood, N (1 February 2003). "The introduction of Xenopus laevis into developmental biology: of empire, pregnancy testing and ribosomal genes". International Journal of Developmental Biology. 44 (1). ISSN 0214-6282
- Fiala, Creator, Autor: Christian (29 March 2018). "Titel: Museum für Verhütung und Schwangerschaftsabbruch - Museum of Contraception and Abortion". en.muvs.org. Retrieved 29 March 2018.
- Bleavins MR, Carini C, Malle JR, Rahbari R (2010). Biomarkers in Drug Development: A Handbook of Practice, Application, and Strategy, Chapter 1, Blood and Urine Chemistry. John Wiley and Sons. ISBN 978-0-470-16927-8.
- "Archived copy" (PDF). Archived from the original (PDF) on 2014-07-14. Retrieved 2014-07-08.CS1 maint: archived copy as title (link)
- Wide L (2005). "Inventions leading to the development of the diagnostic test kit industry--from the modern pregnancy test to the sandwich assays". Upsala Journal of Medical Sciences. 110 (3): 193–216. doi:10.3109/2000-1967-066. PMID 16454158.
- Yalow RS, Berson SA (July 1960). "Immunoassay of endogenous plasma insulin in man". Journal of Clinical Investigation. 39 (7): 1157–75. doi:10.1172/JCI104130. PMC 441860. PMID 13846364.
- Kennedy, Pagan (2016-07-29). "Could Women Be Trusted With Their Own Pregnancy Tests?". The New York Times. ISSN 0362-4331. Retrieved 2016-12-12.
- Vaitukaitis, JL (December 2004). "Development of the home pregnancy test". Annals of the New York Academy of Sciences. 1038: 220–2. Bibcode:2004NYASA1038..220V. doi:10.1196/annals.1315.030. PMID 15838116.
- A Thin Blue Line: The History of the Pregnancy Test Kit. "A Timeline of Pregnancy Testing". National Institutes of Health. Retrieved 15 March 2015.
- Nudd, Ti (9 January 2018). "Ikea Wants You to Pee on This Ad. If You're Pregnant, It Will Give You a Discount on a Crib". Adweek. Retrieved 13 January 2018.
- Media related to Pregnancy test at Wikimedia Commons