The basis of all pregnancy tests is the measurement of the amount of the pregnancy hormone beta-HCG.
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Pregnancy tests distinguish between urine tests and blood tests. In the blood, the beta-HCG detection succeeds earlier than in urine.
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There are some ways why a pregnancy test can be false-positive or false-negative, such as using it too early or taking medication.
The reliability of pregnancy tests with urine is given as 90-99. The further the pregnancy progresses, the more meaningful the test result is. A urine test provides a very certain result of pregnancy about two days after the absence of the menstruation (approx. 14 days after fertilization of the egg).
However, incorrect test results may still occur for various reasons.
Causes of a false-negative test:
- The test was conducted too early at a time when the level of beta-HCG in the urine was not high enough..
- The amount of urine tested was too large or the strip was kept in the urine for too long.
- In late stages of pregnancy, the test may be negative because the concentration of beta-HCG has dropped again.
- Night shift work confuses the hormone balance
Causes of a false-positive test:
- Fertilization and implantation of the oocyte has taken place, but in the first days there has been an incorrect development of the fruit plant (early rod site, very early miscarriage).
- Various cancers lead to an increase in beta-HCG.
- Use of drugs containing HCG (e.g. in case of artificial insemination)
- Rudolf-Müller, E. (2015): Schwangerschaftstest, URL: https://www.netdoktor.de/schwangerschaft/schwangerschaftstest/, Retrieved 18.06.2019
- Weyerstahl, T. & Stauber, M. (2013): Duale Reihe – Gynäkologie und Geburtshilfe, Georg Thieme Verlag, 4th edition
- Kainer, F. & Nolden, A. (2014): das große Buch zur Schwangerschaft, Gräfe und Unzer Verlag, 8. Auflage