Pregnancy test: when to do it and how it works

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Catherine Le Nevez
@catherinelenevez
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Contents

  • 1 How a pregnancy test works
  • 2 When to take the pregnancy test
  • 3 Home or laboratory tests?
  • 4 Pregnancy test: how to use it
  • 5 Early pregnancy test
  • 6 Reliability of a pregnancy test
  • 7 Tests, false negatives and false positives
  • 8 Price of pregnancy tests

Those who are pregnant or already have children know it: the pregnancy test day is probably the most exciting for a woman looking for a child. It is the moment of truth that you cannot escape from. And it doesn't matter if you are in the first, second or third experience: holding that "magic stick" in your fingers gives you a heartbeat and a not indifferent adrenaline rush every time. So let's see what there is to know about these tests, which one to choose, when to do it and so on. 



How a pregnancy test works

The principle is the same in all pregnancy tests, whether it is those you buy in a pharmacy or supermarket, or that carried out in an analysis laboratory: the search for human chorionic gonadotropin (beta Hcg). It is a hormone that is not normally present in a woman's body. It is no coincidence that it is called the "pregnancy hormone" because it begins to be produced about 7-10 days after conception. The hormone is not immediately detectable and therefore it is useless to take a test the day after unprotected intercourse. 

After production begins, beta Hcg double every two days. They peak around 60-70 days after conception, and then drop again and remain stable throughout the pregnancy. This hormone is responsible for the classic pregnancy nausea which is stronger and more persistent when the beta Hcg level is high, therefore in the first trimester. In twin pregnancies the concentration is higher.



Beta Hcg are eliminated in the urine. That is why the home test detects pregnancy in just this way.  

When to take a pregnancy test

In principle, it would be advisable to wait for the delay of menstruation which, in general, is the unequivocal symptom of pregnancy. It is true, however, that when you are "on the hunt", the wait is often unnerving. Today the tests are quite refined and are able to identify even small quantities of the beta Hcg hormone. The test done in the laboratory (therefore on the blood) is the safest, even before the delay.

Let's say that everything depends on the regularity of your menstrual cycle. If you are always on time it will be very easy to identify the first day of the delay, as it will have been easy to calculate ovulation. In the event of an irregular cycle, however, you need to have a little more patience and wait before taking the test. 

Home or laboratory test?

It is every aspiring panciona's dilemma. Better the practical device that you buy at the pharmacy or the blood pregnancy test directly? The first - convenient and fast - is able to detect only the presence of beta Hcg. In short, it only tells us if we are pregnant or not. The second, on the other hand, also gives a quantitative value because it indicates the amount of hormone circulating in the blood. 

The data is important for two reasons. First of all it serves to understand approximately how many weeks of gestation it is and then to calculate the weeks of pregnancy. Secondly, when the gynecologist prescribes to repeat the dosage, one has an idea of ​​the course of the pregnancy. For example, if the beta Hcg do not double every two days or even grow at first, there may be some problem. 


Generally the first step is always that of the test done at home. Later, for added safety, your doctor may suggest doing that in the lab as well. 


Pregnancy test: how to use it

Home tests are very simple to use. The stick is impregnated with particular monoclonal antibodies that recognize beta Hcg and therefore make the test positive. The strip gets wet with urine. It should be placed either directly under the flow or immersed in a container in which you have urinated. The response arrives in a few minutes. Depending on the device used, two lines may appear (even if one is light the test is positive), a cross, a smiley face. 

When to take a pregnancy test? There is no ideal time, you can perform when you want. In the morning, however, the urine is more concentrated and it is therefore more likely to detect the presence of human chorionic gonadotropin. 

Early pregnancy test

For some years now, digital pregnancy tests have been added to the classic sticks, a little more sophisticated. They work in exactly the same way, but they are more sensitive: if the normal test can be done from the first day of delay, these instead are able to "find" the beta Hcg even 5 days earlier than the day on which menstruation should arrive. . In addition, they give information about the week of gestation you are in (1-2 weeks, 2-3 weeks or more than 3).

Reliability of a pregnancy test

If you follow all the instructions on the package well, the reliability of a test is quite high, from 95 to 99%. As mentioned, blood sampling gives the certainty of pregnancy. The investigation methods are a bit more refined and the margin of error is practically non-existent. The only annoying aspect is having to wait for the result. 


Tests, false negatives and false positives

Sometimes a home pregnancy test can give a false negative, that is, you are pregnant, but the test says otherwise. The reasons can be different:


- test carried out too early (the amount of beta Hcg is therefore too low to be detected);
- urine that is too diluted (for example, if you drank a lot of water before the test);
- container not perfectly sterile;
- test expired, defective or stored badly or for too long;
- errors in the execution of the test (for example, the stick is not properly wet with urine);
- taking certain medications.

If you are convinced that you are pregnant or if the delay continues, another test should be taken.

False positives (positive test, but pregnancy not in progress) could be linked to urinary tract infections, medication intake, expired tests, presence of blood or protein in the urine, high levels of luteinizing hormone or ovarian cysts.

Price of pregnancy tests

Digital pregnancy tests are more expensive than classic ones. For example, the Clearblue digital (the one that also indicates the weeks) costs around 15 euros. The "normal" ones, on the other hand, range from 7 to 10 euros. Some are sold in pairs.

The price of the dosage of beta Hcg in the blood varies according to the laboratory of analysis, but the average is around 20 euros. 

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