Although manufacturers of skin tests get out of their way to improve the quality of their products, they cannot foresee all the circumstances associated with the woman’s body and with the external conditions in which the pregnancy test is performed. It is necessary to take into account the accuracy limitations that the testing technology itself imposes.
Home pregnancy tests have become a common method of self-diagnosis for many women. Test manufacturers unanimously claim that their products are free from flaws, and the probability of error does not exceed the statistical error. But is the test you bought at the pharmacy so reliable? Should pregnancy tests be trusted? Can a pregnancy test be wrong?
How does a pregnancy test work? The principle of its work is based on the method for determining the presence of human chorionic gonadotropin in the urine (hCG). HCG is a hormone that is produced by the chorion, the precursor to the placenta. HCG appears in the body as soon as a fertilized egg attaches to the endometrium (implantation occurs).
HCG is necessary to protect the embryo from negative influences, in particular, from the contraction of the uterus, as well as to rebuild the body in the mode of gestation. HCG is found in the blood and urine, where it enters through the kidneys. The level of the hormone after the start of its synthesis is constantly growing, and in geometric progression. And every 2-3 days the amount of the hormone in the urine doubles. The average period from conception to the moment when the concentration of hCG reaches 25 units (the sensitivity level of a typical test) is 10 days.
In home tests to check for pregnancy, antibodies to hCG are present, which react with the hormone, and as a result change their color. This phenomenon can be recorded by the user of the test.
But does this mechanism always work without failures? Could an error occur? First of all, it must be remembered that a pregnancy test only responds to the presence of hCG, and does not show the fact of pregnancy itself. Meanwhile, the hormone can be present in the body even when there is no pregnancy.
What reasons can make a test fail and show a false positive result:
- hormone production by a tumor in an internal organ;
- taking funds containing hCG;
- shortly before the test, premature termination of pregnancy occurred or the woman had an abortion;
- cysts or other tumors of the female genital organs;
- tumors or brain injuries leading to the production of hCG in the pituitary gland;
- delivery that took place shortly (less than 1 month) before the test.
A few words need to be said about the drugs. Many infertility medications contain the hCG hormone. These drugs include Profazi, Pregnil, Ovitrel. HCG is added to the drugs for a reason. This is due to the fact that this hormone allows you to normalize all processes associated with ovulation. Therefore, a pregnancy test can give a false positive result if a woman takes such drugs (especially if she does not suspect about their composition). Moreover, an increased level of the hormone persists in the body for another 2 weeks after discontinuation of the drug. But contraceptives do not affect the level of hCG.
Oddly enough, tests with high sensitivity (10 units) are more likely to show false positive results. And they often perceive episodic hormonal surge in the female body as a state of pregnancy.
Also, home tests give positive results when the pregnancy seems to be there, but it is abnormal.
We are talking about such unpleasant phenomena as:
- frozen pregnancy
- ectopic pregnancy,
- cystic drift.
The most dangerous complication is an ectopic pregnancy. With this pathology, the egg does not attach to the inner surface layer of the uterus – the endometrium, but to some other place, most often to the surface of the fallopian tube. In this case, the fetus does not develop, and the pregnancy ends prematurely. In the most severe cases, a woman may lose the fallopian tube.
Therefore, having received positive test results, rejoice prematurely. It is necessary to make an appointment with a doctor and undergo an ultrasound scan, which is able to detect the fetus and find out its condition.
The test does not show an existing pregnancy
Can a pregnancy test be wrong in this case? Yes, and this situation is much more common than the opposite – when the test informs of a non-existent pregnancy. There can be many reasons, including the banal marriage of the strip. Therefore, gynecologists do not advise using expired strips, those that were stored in inappropriate conditions. It is best to buy test strips not in supermarkets, but in pharmacies, since only in the latter it is possible to create the necessary conditions for storage.
Most often, errors are obtained due to improper use of the tests or because the sensitivity of the test is insufficient.
The testing process in the case of test strips is simple. In the morning, you need to collect urine and, without putting things in a long drawer, lower the strip to a certain mark in the container with urine, hold it in it for several seconds, pull out the strip, put it on an even place and wait for the result for several minutes. Two transverse lines (minus and plus in some models) indicate a positive result, one – negative, zero bars – the pregnancy test did not work.
Nevertheless, every fourth woman manages to do something wrong, most often due to the fact that she inattentively reads the instructions. So you should not rush to blame low-quality products. Indeed, if an analysis using the same test strips is carried out by an experienced person, for example, a gynecologist, then erroneous results are obtained only in 1 case out of 100.
The main technical errors that women make during testing:
- too deep immersion of the test strip in a container with urine,
- insufficient exposure to the strip in the urine,
- overexposure of a strip in urine,
- stale urine is used,
- the test result is read too soon or too late
- the strip after extraction from the liquid is not in a horizontal position,
- a dirty or wet test is used,
- too much time has passed after opening the dough package.
All of the above applies to ordinary test strips. Tablet, inkjet, and digital tests are more error resistant and harder to use when applied. In tablet tests, the strip is enclosed in a plastic case, so it is more difficult to accidentally wet it, and in inkjet strip it can show the correct result even after wetting it with urine during urination. On the other hand, these tests have a higher price.
In addition, you should remember that before the test, certain rules must be followed. You can not drink a lot of water, take diuretics, or even consume diuretic effects, such as watermelons, cherries. The test is best done early in the morning, using urine obtained immediately after waking up. This is due to the fact that before going to bed, urine is more diluted, therefore, the specific content of various substances in it, including and hCG, the smallest. However, a low level of the hormone in the urine can also be observed for natural reasons. For example, if a woman suffers from kidney disease or the fetus is poorly attached to the uterine wall and the hCG hormone is not produced.
A false negative result can be even more dangerous than a false positive. After all, if a test was done, and it showed the absence of pregnancy, but it actually is, then a woman, not knowing about it, can perform some actions that can harm an unborn baby – drink alcohol, take potentially teratogenic drugs, take an X-ray.
Two conflicting test scores in a row
What should I do if one of the tests showed the presence of pregnancy, and the second one, done a few days later, showed its absence? It’s better not to guess which test is right, but to go see a doctor right away. It is likely that the second (or first) test is lying, but other explanations are equally likely:
- the pregnancy, which had just begun to develop, stopped for some reason;
- there is a risk of premature termination of pregnancy;
- condition of ectopic pregnancy.
In all these cases, after the initial increase, the hCG level begins to fall.
What day do you need to test?
The success of the test also depends on the time of the test. The optimal time depends on the sensitivity of the test you are using. Some manufacturers claim that their tests are so sensitive that they can determine the state of pregnancy about 4 days before the next menstruation.
But is it worth the rush? Gynecologists believe not. Here it is worth considering the probability of delaying ovulation for several days. Only after a woman has found that her menstruation is delayed does it make sense to conduct testing. And not even on the first day of menstruation, but after waiting a bit, for example, 4-5 days. At this time, the probability of detecting hCG is approaching 99%.
If finances allow, then a woman can buy several tests at once and conduct testing every day, starting from the domain-building period. In this case, even if the first tests turn out to be negative, then there will be nothing wrong with this, since subsequent ones may bring more favorable news. Moreover, frequent testing does not affect the health of women. In this regard, false negative results are not as unpleasant as false positives, since in most cases they are associated only with insufficient sensitivity of testing tools.
What tests are best to choose?
Are all tests the same? What kind of tests do you prefer? Which manufacturer’s tests are the most reliable? What tests are less likely to be mistaken? All manufacturers, of course, praise their products and prove that competitors are not suitable for them. However, in fact, the quality of tests of several leading manufacturers is approximately the same. However, there is a certain difference between the different classes of tests. Not all of them make mistakes with the same frequency. Consider the categories of tests in terms of their reliability.
|Test category||probability of error caused by user actions||probability of misinterpretation of test results||usability test||test cost|
|Inkjet electronic test||low||low||high||high|
On the one hand, electronic and inkjet tests are extremely reliable. But, on the other hand, they are very expensive. Perhaps it would be wiser to purchase several inexpensive strips from different manufacturers and conduct testing with all of them at the same time. As a result, we also get a more or less objective picture. Even if the stripes 1-2 are spoiled, the rest will show the correct result.
The Achilles heel of the test strips, in addition to low sensitivity, is also the difficulty of interpreting the results. Although the instructions for any such test say that the second line of low intensity should be counted as a positive result, this does not convince many women. Therefore, they have to wait until the level of hormones rises to an acceptable level in order to conduct a second test that would dot the “i”. Electronic tests do not have such a drawback – the task of interpreting the results is assigned to the chip built into the test. And the results are displayed in the form of unambiguous answers “yes” or “no”, “pregnant” or “not pregnant”.
The most advanced variety of electronic tests are reusable. They have several replaceable cartridges, so a separate test will not be as expensive as in a one-time electronic test. Many electronic tests allow you to calculate the gestational age to the nearest week.
Also, tests differ in their sensitivity. It is usually indicated on the test packaging. This parameter in most cases is 10-30 units. The number indicates the concentration of the hormone that the urine test can detect. Therefore, the smaller the number, the more sensitive the test. However, in practice, not everything is so simple. Manufacturers often indicate a sensitivity that is clearly overstated compared to this. Therefore, if you choose between the “low-sensitivity” test of a well-known brand and the “highly sensitive” test of dubious origin, then you should prefer the first, since in practice it may even be more sensitive.
In addition, when going to the pharmacy for a test, you must not forget to check the expiration date and integrity of the package.
It is not worth completely relying on any test device. The most reliable methods of checking pregnancy are blood tests for hCG and ultrasound of the uterus. All of these methods are available only in medical facilities. Therefore, no matter how good the test would be, you can’t do without a doctor’s consultation. Ultrasound of the uterus is able to show the presence of pregnancy no earlier than a week after pregnancy is delayed. But a blood test for hCG is more sensitive than a urinalysis. But ultrasound can easily identify any defect in the development of the fetus.