Pregnancy tests are of two types:
- home (urine analysis at hhome);
- clinical (blood test in the hospital).
Both home and clinical tests check the same thing — the presence of human chorionic gonadotropin hormone (hCG) in biomaterial (urine or blood). HCG is produced by the cells that eventually form the placenta.
Why do tests determine pregnancy by hCG?
This is the simplest and most reliable pregnancy indicator. It is secreted by the cells of the embryo and the future placenta. As soon as the fertilized egg is implanted into the mucous membrane of the uterus, the hormone enters the blood (sometimes this happens as early as 6 days after fertilization of the egg). After that, the HCG level increases very quickly: it doubles every 48 hours until a period of 14 weeks. Gradually, excess hCG begins to be released into the urine, and there it is detected by home tests.
When to take a pregnancy test?
After ovulation, the egg’s path from the ovary to the uterus takes about a week. It can be fertilized at any time: either in the fallopian tube, or upon reaching the uterus. But HCG production begins only after implantation of fertilized eggs into the uterine wall.
It is difficult to predict exactly when fertilization took place: spermatozoa can live in a woman’s body for up to 5 days. It is for this reason that most home pregnancy tests advise women to wait: it is better to do the test on the second or third day of delay or about 15-16 days after ovulation.
If the cycle is unstable, the ideal time for the test is determined differently: If menstruation occurs at intervals of less than 21 days or more than 35 days, and if their periods vary from month to month, cycles are considered irregular. In these cases, a pregnancy test should be done 36 days after the beginning of the last menstruation or 4 weeks after the last unprotected sex.
The test is negative. So there is no pregnancy?
This is not the case: the test may be false negative. If, a few days after the negative result, the monthly period has not appeared, repeat the test. The second negative result will be more reliable, but even a weak second strip should be treated as a positive test.
Why do the instructions recommend taking the test in the morning?
The probability of getting a reliable result is higher when the biomaterial – urine – is the most concentrated: there is more hCG in it. It happens in the morning. Therefore, most tests recommend doing a test immediately after waking up, on the second day after missing menstruation.
Are there any alternatives to pregnancy tests?
Among the exact tests, there is only a blood test for HCG. No folk tests (with soda, iodine, potassium permanganate or boiling urine) are unreliable. Modern tests remain the most reliable and easiest way to determine pregnancy.
How accurate are pregnancy tests made at home?
Home pregnancy test kits claim that, when used correctly, they have an accuracy of 97 to 99%.
An important indicator in this matter is sensitivity. It can be determined by the test box: the smaller the number indicated on the package, the more sensitive the test. For example, a test with a sensitivity of 20 IU/l (international units per liter) determines pregnancy at earlier stages than a test with a sensitivity of only 50 IU/l.
The cost of a pregnancy test can also be a sign of its sensitivity: more expensive ones, as a rule, allow you to detect pregnancy earlier.
Why can the test be wrong?
Several factors can affect the accuracy of a home pregnancy test:
- the time of taking the test. If you take the test too early after the intended conception, the test will show a negative result.
- violations of the instructions. If you do not follow the instructions, you may miss an important detail of testing and get a false result.
- physiological features. Some women simply do not produce so much hCG hormone during pregnancy that it can be detected by home tests. In this case, pregnancy can only be determined by a blood test.
Remember: false positives or negative results are always possible with any test. It is best to confirm the test twice and consult a doctor.