If you suspect you’re pregnant, a pregnancy test can quickly provide clarity. However, timing is crucial for a reliable test result. We explain the optimal timing and how to reduce the risk of false-negative results.
How do pregnancy tests work?
To determine the optimal time to test, it’s important to understand how pregnancy tests work. They measure the concentration of the hormone hCG (human chorionic gonadotropin) in either the blood or urine.
The hormone is a clear indicator of pregnancy, as it is only produced after a fertilized egg has implanted in the uterine lining.
In addition to the different methods of application, the difference between blood and urine tests also lies in their sensitivity – that is, at what point a test indicates pregnancy.
Urine test: Pregnancy test for home
Those who want to perform the test themselves can use the classic urine test. This is easy to perform while using the toilet and provides results within minutes. Urine tests usually detect pregnancy once a period has stopped.
A major advantage of urine tests is that they are comparatively inexpensive and easily available—e.g., in drugstores, supermarkets, pharmacies, or online. Price differences don’t necessarily reflect their overall reliability, but often reflect their sensitivity and ease of use.
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Blood test: Early detection by the doctor
Pregnancy can be detected in the blood as early as 6 to 8 days after fertilization. This makes blood tests significantly more sensitive than urine tests. They also provide accurate hCG levels, allowing the pregnancy’s progress to be determined more accurately.
A urine test is usually sufficient as an initial test. A blood test at a doctor’s office is recommended for anyone who:
- have already had a positive urine test
- want certainty as early as possible
- Want to avoid application errors
- or medical questions.
If you are pregnant, there are numerous options for prenatal care.
When is a pregnancy test reliable?
The reliability of a pregnancy test depends largely on the timing and type of test. After fertilization, it takes about 6 to 12 days for the egg to implant in the uterine lining. This also triggers the production of the pregnancy hormone hCG, which can then be detected in the blood. HCG levels then rise rapidly in the first weeks of pregnancy, doubling approximately every 48 to 72 hours.
HCG is only detectable in relevant amounts in urine later. Therefore, most commercially available urine tests are most reliable starting on the second day of a missed period. Ideally, first-morning urine should be used for testing, as this is when the hCG concentration is highest.
Early tests: possibilities and limitations
Early pregnancy tests react to even small amounts of the pregnancy hormone hCG and can therefore theoretically detect pregnancy as early as 4 to 5 days before the expected period. However, there is also a higher risk of false-negative results. In a study on the reliability of early pregnancy tests, over half of the early pregnancy tests examined failed to conclusively detect pregnancy.
This means that a negative test result from an early pregnancy test does not always definitively rule out pregnancy. A second pregnancy test at a later date, or if in doubt, a visit to the gynecologist, is generally advisable after an early pregnancy test.
An early test can still be useful in certain situations:
- In case of urgent medical need
- Before taking medication that could harm an embryo
- In case of strong psychological pressure due to uncertainty