All pregnancy tests beta hCG hormone used to diagnose an ongoing pregnancy. This makes sense, because this hormone begins to be produced by cells of the embryo in the first days after conception. In general, it is recommended to do the test only after the delay period, as it is at this time about the levels of beta hCG are high enough to be detected by pregnancy tests. The delay period itself has nothing to do with the levels of beta hCG. It is only a coincidence that, in most women, beta hCG levels are high enough to be detected around the end of the menstrual cycle, ie, at the time that menstruation should lower. We will explain in more detail.
Ovulation usually occurs in the middle of the menstrual cycle. This means that most women ovulate about 14 days before the end of the cycle. As the life of the egg is only 24 hours, it needs to be fertilized in this short period; otherwise, pregnancy does not occur. That being so, when a woman is pregnant the egg is fertilized about 14 days before the date set down for the next period.
Therefore, in the best case, the hormone hCG begins to be produced 6 days after fertilization in the worst case, 12 days after fertilization. Only by this explanation and you can understand why it makes no sense to do a pregnancy test a few days after unprotected intercourse. If you have not yet started the production of CG by the embryo, there is no way the pregnancy test has positive result.
After the start of production of hCG are needed a few days for her to reach a sufficient blood concentration that can be detected by the most sensitive blood tests. This means that even in the best of cases which is an embryo implantation in the uterus around the 6th day after conception, are necessary other 2 to 4 days for there to be significant amounts of hCG in the blood.
Consequently, in the best case, hCG is detectable only 4 to 6 days before the period down. In most cases however, the embryo is not implanted so soon and the time that hCG is detectable is only 1 or 2 days before the expected date for the next period. And we can not forget that there are cases of delayed implantation, which makes the hCG only becomes positive after the menstrual delay.
Blood tests can detect hCG beta concentrations up to 20 smaller than urine tests. Moreover, for beta hCG appears in the urine, it is necessary that hCG in the blood is in relevant concentrations. Therefore, the blood test becomes positive a few days before the urine test and can be positive even before menstrual delay. However, as the test drug is much easier to do, provides a result almost that instant, does not require needle sticks and is able to detect the beta hCG few days after the blood test, it ends up being the option simpler for anyone who wants to know if you are pregnant or not.
The causes of false positive pregnancy test ie, a positive result in a woman, who is not pregnant, are rare. Therefore, in principle if a pregnancy test, urine or blood is positive we believe that the woman is actually pregnant. On the other hand, a false negative pregnancy test, ie a test with a negative result in a pregnant woman, it is relatively common, especially if the test is being done before the menstrual delay. In these cases, the test is negative not because the woman is not pregnant, but because the level of hCG produced by the embryo is still so low that the tests cannot detect it. False negatives are more common in urine tests on blood tests.
Blood tests usually have positive pregnancy between the 8th and 13th day after conception (i.e., 1 to 6 days before the menstrual period). From the first day of menstrual delay, the possibility of pregnancy blood test have tested positive is 99%. If your period is late one day and the blood test is negative, the possibility that you are pregnant is very low. If by chance you are having symptoms of pregnancy and do not convince yourself that you are not pregnant, you can repeat the test after 5 days. Sometimes, she misses the calculation of their cycle and thinks your period is late when it is not yet. This is common in women with irregular cycles. In these cases, the blood test can really give false negative.
Pregnancy tests done at home, either with bleach Coca-Cola, vinegar, toothpaste or other home product, are unreliable and not used to diagnose or rule out pregnancy. These tests have no scientific basis and can cause damage as the urine reaction with chlorine or bleach can release toxic gases. Yes, unless you are mistaken regarding the date of commencement of the period. If you think that menstruation is delayed by 7 days but it really is with only 1 or 2 days late, it may be a false negative.
If the woman has a very irregular cycle or is not accompanying the dates of menstruation to know when to get the next period, you should do a pregnancy test, at least 21 days after the sexual relationship that could lead to a pregnancy. If the woman had multiple relationships in this period, you count the interval since the last unprotected. Obviously, if menstruation downs before the 21st day no need to do the test as this indicates that the woman is not pregnant.