Pregnancy tests allow a woman to find out about the onset of an "interesting situation" in the early stages. The manufacturers of all test systems without exception claim that their products guarantee high accuracy of results.
Nevertheless, women often report errors - in the presence of pregnancy, the test did not show it, and in the absence, it gave a false positive result. Why this happens, and how to improve the efficiency and accuracy of testing, this article will tell.
Operating principle
Before talking about the possibility of a pregnancy test error, you should be clear about how it works. Most test systems are designed with the ability to determine a specific hCG hormone in a woman's urine. Chorionic gonadotropin begins to be produced in a woman's body only after the embryo is implanted into the endometrial layer of the uterus.
After fertilization, the zygote, continuously splitting up, begins to move towards the uterine cavity. It passes the fallopian tube, descends into the uterus, and remains free for several days. All this usually takes about 7-9 days. During implantation, the ovum sticks to the endometrium, after which the chorionic villi begin to produce an enzyme that destroys endometrial cells. So the embryo gets the opportunity to plunge into the inner layer of the genital organ deeper.
As soon as the implantation is completed (approximately 40 hours after the beginning of adhesion), the chorionic villi are connected to the blood vessels of the female body. The baby begins to receive nutrients and oxygen from the blood of the future parent, and doses of chorionic hormone begin to enter the woman's blood.
The amount of hCG increases by 2 times every 48 hours. If the pregnancy is multiple, and there are two embryos, then the concentration in the allotted time increases 4 times, and if a woman conceives triplets - 6 times. In urine, the concentration of hCG begins to increase a little later than in the blood.
Chorionic gonadotropin - the most important hormone during pregnancy... It does not allow the corpus luteum to fade away - a temporary gland that was formed at the time of ovulation at the site of a bursting follicle on the surface of the ovary. The corpus luteum diligently produces progesterone to ensure the correct hormonal levels in the second phase of the cycle and early pregnancy. A high concentration of progesterone is the key to successful bearing of a baby.
This hormone relaxes the muscles of the uterus, prevents it from toning, increases the energy and fat reserves of the woman's body, prevents menstruation, and also partially reduces the woman's immune defenses so that immune cells do not destroy the embryo.
In the absence of pregnancy, the corpus luteum dies 10-12 days after ovulation, and a decrease in progesterone levels leads to the onset of menstruation. After implantation, high doses of hCG keep the gland in working order, and therefore menstruation does not come.
Thus, the manufacturers of most tests base the diagnosis on the determination of the amount of hCG in the urine. For this, a reagent is applied that is sensitive to the presence of chorionic gonadotropin in certain quantities. If the target substance is found in the urine, the test reacts to this with a second strip.
Timeline for getting correct results
The chemical has been applied to the absorbent portion of the test strip. Thus, having received two clear strips, a woman can regard this as a positive result, indicating that chorionic gonadotropic hormone is present in her urine in a concentration exceeding the norm for non-pregnant women and men (this norm is from 0.0 to 5.0 mU / ml). Already 12-14 days after conception in the urine, the level of hCG can exceed 20 mU / ml, and after a delay - 40 and higher units.
Considering that the tests are different in sensitivity, even the most insensitive test (25-30 units) determines the presence of hCG on the first day of the delay or later. Ultrasensitive test systems (10-15 units) catch hCG traces according to their threshold of perception, sometimes 2-3 days before the start of the delay. From the first day of delay, the results are as accurate as possible.
Thus, with a delay of 3 days or more, the accuracy remains high. The result is displayed correctly, of course, provided that the woman has followed all the requirements of the self-test instructions.
Recent research by scientists has shown that the accuracy of the tests begins to decrease after 6 weeks of pregnancy, when the concentration of hCG becomes very high. In this case, the error probability starts to be 5%. But at such a long time, there are others, more informative, able to find out the fact of pregnancy - ultrasound, gynecological examination, blood test for hCG from a vein.
In cases when you want to know about pregnancy as early as possible, you should opt for ultrasensitive tests or electronic systems - they are less likely to "lie" in the period before the start of the delay. But the minimum period for which a test should be done to obtain a true result is not earlier than 2-3 days before the expected start date of the next period.
Correct (positive, positive) is the result, in which a woman sees two clear, bright stripes after the prescribed time.
Types and rules of use
As already mentioned, modern pharmacists offer a variety of types of test systems, but the more difficult it can be to make a choice. Each of the types needs to be clarified the rules of use if a woman wants to get the most accurate result.
As a general rule of thumb, don't focus on cost. Sometimes a cheap test gives more accurate and early results than an expensive system. Which type to choose is up to you, because each type has its own nuances.
Strip strips
This is the most popular and inexpensive test type. There is nothing surprising in the fact that every second lady gives preference to just such systems. They are not difficult to use. The level to which the test is to be immersed in the previously collected urine is marked on each strip. Hold the strip vertically in the urine to the specified level for as long as the test manufacturer recommends (the information is on the package, usually 10-30 seconds).
Then the strip should be placed horizontally on a dry surface, for example, on a clean paper towel, and after 5 minutes evaluate the result.
You cannot dip the same strip into urine several times in a row, these tests are one-time. Dispose of the strip after use.
How accurate are these tests? If they are done at the optimal time (see above), then the accuracy is up to 95%. This is not 99% declared by the manufacturers, but still a completely satisfactory result. Could they be wrong? Yes they can. And there may be many reasons for this - from too early self-diagnosis (when the level of hCG in the urine has not yet exceeded the system's sensitivity threshold) to trivial errors during testing (holding the strip in liquid for too long, waiting too long for the result, immersed the strip deeper than need to).
The disadvantages of such tests are quite obvious: you have to collect urine, look for a suitable "container" for this.
Although today you can buy a set of strips (5 ovulation tests + 2 pregnancy tests). These kits often include seven single-use small containers for urine collection.
Tablet
It is believed that the results of such systems are slightly higher than those of strip strips, although they can be wrong. Increased accuracy is achieved due to the design of the system: the part with the applied reagent sensitive to hCG is protected by a plastic box. It is necessary to bury a urine sample in the test with a special pipette, it is included in the kit, so you don't have to invent anything... The urine must get into into a special window-receiver. After 5-10 minutes (depending on the manufacturer's recommendations) the result will be displayed.
Tablet tests are somewhat more expensive than strip strips, but women say they are much more convenient to use. Although not everyone agrees with this opinion - it is easier for some to dip the strip into the liquid than to bury it with a pipette exactly in a limited window.
Jet
A very convenient option for women who value their time, and every minute counts. There is no need to collect any urine for self-diagnosis. The cap is removed from the system, and at the moment of handling a small need, the test part of the device is placed under the stream. After a few minutes, the result is displayed.
The main difference from the two previous types is that the test can be carried out absolutely at any time of the day, without a clear indispensable link to the morning urine portion... If convenient, you can do it in the evening, at night or in the afternoon. Also, inkjet systems have slightly higher accuracy, they are less likely to make mistakes.
There are reusable digital inkjet systems in which only test strips need to be changed. There are quite a few ultra-sensitive inkjet models that are the preferred choice for diagnosing a "position of interest" before a delay occurs.
Digital (electronic)
The principle of operation is not much different from those described above, but the difference is that the system is always reusable. The cost is much higher than the above budget options. But there are not so many options for errors, these tests are considered today one of the most accurate (98-99% - the accuracy of determining the fact of pregnancy, up to 90% - the accuracy of determining the gestational age in weeks). Not all tests set the deadline, only some models.
Among this category of tests, most of all models with a high threshold of sensitivity, which means that already 3-4 days before the expected menstruation, a woman can get a reliable result.
When do tests fail?
There is no system in nature that will answer your questions with an accuracy of 100%, and this is the main thing that you need to know when starting a self-diagnosis. There are several options for the results you can get:
- positive (two clear stripes);
- weakly positive (the second stripe is weak, pale);
- false positive (positive or weakly positive result in the absence of pregnancy);
- negative (one bar);
- false negative (one strip in the actual presence of pregnancy).
The following factors affect the percentage of error probability:
- how suitable the system is for diagnostics (whether the rules for storage, transportation, implementation of the system are followed, is the test expired);
- how correctly a woman conducts testing, whether she complies with the rules and requirements of the instructions for use;
- whether the woman took a large amount of any liquid 4-5 hours before testing (urine becomes less concentrated, and the total total content of human chorionic gonadotropin decreases);
- how long before testing was urine collected (ideally, material should be collected just before diagnosis);
- Is the timing right for testing.
And also a lot depends on the type of test chosen. More accurate electronic and inkjet strips, less accurate and more likely to make mistakes.
False positive and false negative results, as well as weak positive ones, are more likely to be erroneous than clear positive or negative results.
Such results require additional confirmation or refutation of the result. Bearing in mind that the level of hCG increases gradually, it is worth retesting after two days (during this time, the level of human chorionic gonadotropin will double).
Causes of errors
The reasons why a test can give an incorrect, incorrect result are numerous. The problem may be in the system itself - a poor-quality or expired test cannot guarantee any intelligible result. Pay attention to the tightness of the bag in which the product is packed. It shouldn't be violated.
But the most common reason women get the wrong results is in haste. Women start testing too early, not taking into account the fact that ovulation could be late, and it is rather difficult to adjust the implantation time to some norms (the embryo can be attached on the 6th day after ovulation, and on the 10th day). Respectively, with late ovulation or late implantation, the test will show two strips much later, possibly even after a delay.
Sometimes tests are "kinky" for endocrine diseases in women associated with imbalance of sex hormones. Sometimes a high level of hCG in the absence of pregnancy is a sign of a developing tumor, and this will not be related to pregnancy, although the system will most likely show slightly positive results.
Another reason a woman may get incorrect results is taking hCG medications. If ovulation was stimulated, if a woman became pregnant in the IVF protocol, there is no hope for tests - they can falsely react to traces of chorionic gonadotropin, injected in an injection form to accelerate the maturation of eggs.
Often a false positive result appears in the following cases:
- the diagnosis was carried out in the period after childbirth, during the next cycle after an abortion or surgery to eliminate an ectopic pregnancy - the level of hCG can remain elevated for several weeks in the absence of pregnancy;
- when treating with drugs containing chorionic gonadotropin in the current cycle;
- with hormone-dependent tumors in the body.
A false negative result can occur if:
- the test was done too early, the hormone in the required amount did not have time to accumulate either in the blood or in the urine, and the test simply does not catch an insignificant amount of it;
- diagnostics was carried out after heavy consumption of liquid or products containing it;
- diagnosis is carried out against the background of taking diuretics.
A dubious test (with a dim second strip) is the most alarming for the fair sex. How to understand it? There are two options:
- either the woman is pregnant it's just too early for testing, and the hormone is determined by the reagent, but in a small amount, so there is no bright staining of the strip;
- either the woman is not pregnant, in which case it is imperative to consult a doctor, to be examined for hormonal disorders and neoplasms.
A faint streak may remain after the delay. In this case, you also need to go to the doctor - an ectopic pregnancy, undeveloped pregnancy is not excluded (while hCG continues to be produced until a certain period, but in negligible quantities). Weakly positive results are possible in a woman who becomes pregnant during lactation.
With breastfeeding, if the cycle has already recovered, the production of prolactin is increased, which reduces the production of progesterone, respectively, and the level of hCG may be reduced (but this is not necessary). In any case, if you receive a weak positive result while breastfeeding, you need to consult a doctor and undergo an examination.
How can I check the result?
The test may show two strips or not show them, but if there is no menstruation at the expected time, you should consult a doctor. The reasons why menstruation may not be there are numerous and not at all harmless. In some cases, treatment is needed to eliminate hormonal imbalance, ovarian dysfunction or inflammatory diseases.
If the results are questionable, and there is an assumption that the system could cheat, you need to repeat the test after two days (following the rules, instructions and recommendations of the manufacturer). If there is no strength to wait, then it is better to go to the clinic and donate blood for hCG.
In the blood, the content of this hormone grows faster, and already 3-4 days after implantation before menstruation, in 4-5 days it is possible to establish the fact of pregnancy with high accuracy.
You should not rely on your own symptoms and sensations - they are very deceptive and are often far-fetched or have nothing to do with pregnancy... One week after the start of the delay (not earlier), you can visit the ultrasound office, and two weeks after the delay, you can visit the gynecologist and undergo a gynecological vaginal examination.
Folk methods (dipping a drop of iodine or a spoonful of soda into the urine) cannot confirm the results, since, in general, they are anti-scientific. Both iodine and soda react to the acidic environment of urine, not hormones.
