The basis of all pregnancy tests is the determination of the concentration of the pregnancy hormone beta-HCG.
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At a glance
Pregnancy tests distinguish between urine tests and blood tests. In the blood, the beta-HCG detection succeeds earlier than in urine.
Beta-hCG stands for human chorionic gonadotopin and is a hormone produced by part of the placenta. It ensures the onset and maintenance of pregnancy and is therefore well suited to prove pregnancy. In the blood it is detectable about 6-9 days after conception, in the urine only after about 2 weeks. The delay is due to the fact that it must first pass through the bloodstream to the kidneys and then be excreted in the urine.
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).
There are a few ways why a pregnancy test can be false-positive or false-negative. These include the premature use or the intake of medication. The following causes can also lead to incorrect test results:
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 medications containing hCG (e.g. in the case of artificial insemination)
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