When Do Pregnancy Test?

How many days of pregnancy can I already take a pregnancy test? How many days after conception pregnancy test becomes positive? Is it really necessary to wait for the missed period? I can make the home tests before performing the pharmacy test?


We have several articles about pregnancy and pregnancy diagnosis on our site, but none of them focuses on the right time to take a pregnancy test. The questions listed above have been made with some frequency by our readers, which is why we decided to write a unique article on when to do the pregnancy test. In this article we'll explain how many days of pregnancy are needed so that the result of the pregnancy test becomes reliable.

After all, if a woman is already pregnant, why the tests give negative in the early days and pregnancy?

There is no single answer to this question because it depends on the size of the woman's menstrual cycle and the moment that occurred fertilization. However, since most women have a cycle with approximately 28 days, each with a few more days, others with few days unless the moment a pregnancy test becomes positive it will not vary much in most cases.

All tests utilize the pregnancy hormone Beta HCG as a way to diagnose an ongoing pregnancy. This makes sense, because this hormone begins to be produced by the embryo cells in the first days after conception.

In general, it is recommended to take the test only after menstruation been delayed, it is around this time that the beta hCG levels become high enough to be detected by pregnancy tests.

The menstrual delay itself has nothing to do with the Beta hCG levels. It is merely a coincidence that, for most women, the levels of beta-hCG only become sufficiently large to be detected around the end of the menstrual cycle, namely the time period that should appear. We will explain in more detail.

Ovulation typically occurs in the middle of the menstrual cycle. This means that most women ovulate about 14 days before the end of the cycle. As time ovum's life is only 24 hours, it needs to be fertilized in this short period of time, otherwise there is no pregnancy occurs. So when a woman becomes pregnant, the egg is fertilized about 14 days before the scheduled date of the next menstrual down.

Once fertilized, the zygote (product of fertilization of egg by sperm) migrates the tubes toward the uterus. This migration takes 6 to 12 days. During this time the zygote becomes an embryo develops, and the trophoblast, a group of cells that will give rise to the placenta. It is the trophoblast those who produce the hormone hCG. This production, however, only begins when the embryo implants itself into the wall of the uterus.

So at best, the hCG hormone starts being produced six days after fertilization; at worst, 12 days after fertilization. Just for that explanation now you can understand why no point do the pregnancy test a few days after having unprotected sexual intercourse. If not already started the production of hCG by the embryo, there is no way any pregnancy test to be positive.

After the start of production of hCG, it takes a few days for it to reach a sufficient blood concentration that can be detected by the most sensitive blood tests. This means that even at best, which is an embryo implantation in the uterus around the 6th day after conception, it takes a few extra 2-4 days to have significant amounts of hCG in the blood. Consequently, at best, only hCG becomes detectable 4 to 6 days before menstruation down. In most cases, however, the embryo does not implant up so early, and the time that hCG becomes detectable is only 1 or 2 days before the expected date of the next menstruation. And do not forget that there are cases of delayed deployment, which makes the hCG only become positive after the missed period.

There are only two types of trusted pregnancy tests: the dosage of the beta hCG in blood and pharmacy Tests that detect the presence of hCG in urine. The most reliable test is surely the blood of hCG dosage. This test is more reliable so that even if you have a positive test pharmacy, is indicated to the blood test to confirm the result.

Blood tests can detect hCG beta at concentrations up to 20 smaller than urine tests. In addition to the beta hCG appear in the urine, is necessary before the blood in the hCG is in relevant concentrations. Therefore, the blood test becomes positive few days before the urine test could be positive even before the menstrual delay.

However, as the pharmacy test is very simple to be made, it provides a form result almost instantly, does not require pricked with a needle and is capable of detecting beta hCH only a few days after the blood test, it ends up being the simpler option for those who want to know if you are pregnant or not.

The false positive pregnancy test causes, ie, a positive test to a woman who is not pregnant, are rare. Therefore, in principle, a pregnancy test, either urine or blood, positive der, we believe that the woman is indeed pregnant.

In contrast, a false negative pregnancy test, ie, a negative test to a pregnant woman, it is relatively common, especially if the test is done before the missed period. In such cases, the test is negative is not because the woman is not pregnant, but because the level of hCG produced by the embryo is still so low that the tests can not detect it. False negatives are more common in the urine tests than in blood tests.

The blood pregnancy tests usually become positive between the 8th and 13th day after conception (i.e., 1 to 6 days before the menstrual delay). From the first day of menstrual delay, the chance of blood pregnancy test to be positive is 99%. If your period is late one day and the blood test was negative, the chance of you being pregnant is very low. If by chance you are having symptoms of pregnancy and not be convinced you are not pregnant, the test can be repeated after five days. Sometimes the woman misses the calculation of its cycle and ends up finding that the period is late when it is not. This is common in women with irregular cycles. In these cases, blood testing can really give false negative.

But the pharmacy pregnancy test is not as simple to interpret. There are dozens of different brands, some of them more sensitive than others to detect the beta hCG. Some brands can detect the beta hCG with one day of missed period in 97% of pregnant women, but there are others whose sensitivity is only 54%, ie 46% of pregnant women will have a false negative. So for a pharmacy pregnancy test is really reliable, ideally only do it with five days of missed period. The pharmacy test can even be done after 1 day late, but if he comes negative, you need to repeat it after one week because the chance of a false negative is not low.

As we explained in detail in the article: Pregnancy Test domesticated - Myth or Truth, pregnancy tests done at home, either with bleach, Coca-Cola, vinegar, toothpaste or any other home product, are unreliable and not used to diagnose or rule out a pregnancy. These tests have no scientific foundation and may even do harm, because the reaction of the urine with chlorine or bleach can release toxic gases.

So if you think you may be pregnant, said not do home pregnancy test. The correct behavior is to go to the drugstore to buy a real pregnancy test.

I'm using a contraceptive method, the time to do the pregnancy test can be changed?

No, no contraceptive method prejudice the outcome of the beta hCG.

Any medication can prevent pregnancy test to be positive?

No, no medicine prejudice the outcome of the beta hCG in order to make it negative in pregnant women.

Negative pregnancy test after 1 week of menstrual delay is definitive?

Yes, unless you have the wrong date of the coming of menstruation. If you think that period is late 7 days, but it is really only 1 or 2 days late, there may be a false negative.

If I do not know the date of the next menstruation, when I do a pregnancy test?

If the woman has a very irregular cycle or is not keeping the dates of your periods to know when the next period to come, the pregnancy test should be done at least 21 days after having sex that could lead to a pregnancy. If the woman had multiple relationships at this time, the interval should be counted from the last unprotected. Obviously, if the menses come down before the 21st day, it no longer has to take the exam, as this indicates that the woman is not pregnant.