Before the invention of pregnancy tests, mankind resorted to various methods of guessing the onset of the gestation period. Peculiar pregnancy tests were carried out by wetting the female urine with grain, mixing urine with wine, changing the characteristics of the biological fluid under the influence of various additives, as well as injecting it with a certain type of frog. So, it was believed that with the onset of pregnancy, wheat or barley grains, sprinkled with urine, sprout faster, which helped not only to diagnose a successful conception, but also to predict the sex of the child. Repeating such a test in the 70s of the 20th century showed a 70% effectiveness of the method for determining pregnancy.
A modern pregnancy test makes it possible to determine the beginning of the birth of a new life without lengthy experiments with various compositions and grains. The variety of tests for express diagnostics, however, implies the need to know when to do a pregnancy test, how to interpret the result and which tests are better to use.
Principles of express tests for home use
Despite the modernization of diagnostic methods, the material for testing remains the same as in the Middle Ages. Urine contains human chorionic gonadotropin, the same hormone, the concentration of which is evaluated in the diagnosis of pregnancy by a blood test.
In the venous blood, the hCG hormone begins to be determined 2-3 days after the start of the introduction of chorionic villi to the walls of the uterus. Chorionic gonadotropin reaches a concentration sufficient in most urine for most tests, about a week after the start of its production in the body.
If there is a concentration of hCG in the urine sufficient for the sensitivity level of the test, a chemical reaction occurs on the surface of the test and the hormone. In the absence of the hormone or its insufficient concentration, the reaction does not occur, and the result is negative.
The average sensitivity of the tests on the market is 25 mUI, and this hCG reaches, as a rule, two weeks after fertilization. Existing tests with higher sensitivity, responding to less hormone, diagnose its appearance 3-4 days earlier.
When can I use the test with a regular cycle of menstruation?
If the menstrual cycle is characterized by regularity and a constant number of days between the onset of bleeding, then it is not difficult to calculate the period of ovulation. The middle of the cycle (with a standard cycle of menstruation of 28 days - on day 14) the egg is released.
Ovum fertilization is possible for three days, its life cycle. After the process of merging the egg and sperm for 4-5 days, the germ cells migrate through the uterus to the placentation site, after which the production of hCG begins. Assuming fertilization within 2 days, 4 days of migration and the time required to achieve the desired concentration of the hormone in the urine, highly sensitive tests are able to show pregnancy 10 days after ovulation, that is, with an average cycle of 28 days - on the 24th day of the cycle . For greater certainty, experts recommend using a highly sensitive test 12 days after the egg leaves the ovary, tests of normal sensitivity - after 15-16 days.
Diagnosis of pregnancy with an irregular cycle
If the menstrual cycle does not differ in regularity, the duration of the periods between menstruation varies, then the time of use of the test depends on the date of ovulation.
Ovulation can be determined by subjective sensations (some women feel characteristic tingling in the area of one of the ovaries, a feeling of fullness, swelling, sensitivity, mood changes), as well as by measuring the rectal temperature and using the ovulation test. When determining the onset of ovulation and possible fertilization, a pregnancy test is used 15 days after the established date.
Morning is wiser than the evening: when is it better to do a test
Most modern test strips do not limit the diagnostic period to any time of the day: they can be used in the morning, afternoon, or night. However, experts, given the possibility of a natural decrease in the concentration of hCG after drinking a large amount of liquid, recommend resorting to diagnostics in the morning, using the first portion of urine after a night's sleep, especially with a small probable gestational age.
During the day, when fluid enters the body, the concentration of the hormone decreases. For periods of more than 18 days after ovulation, this factor is not critical, but the timing of ovulation also does not always coincide with the expected. For accurate indicators, it is better to follow the recommendations of specialists, and in a situation where the test must be carried out in the afternoon or in the evening, the diagnosis will be optimal after four hours of abstinence from a toilet and limited use of liquid products to maintain the level of hCG concentration.
Rules for using express tests
- Follow the test storage rules provided by the manufacturer.
- Using the test in damaged packaging may distort the diagnostic results.
- The package is opened immediately before the diagnosis.
- Using an expired test leads to incorrect results.
- The optimal test time is morning, immediately after a night's sleep.
- If the test is not an inkjet test, collecting urine requires the use of a clean container.
- It is recommended before testing to conduct hygiene procedures with washing the external genital organs.
- Strictly follow the instructions for use.
Pregnancy test: instructions for use
There are various types of rapid tests. Instructions for each type are attached to the test, violation of the rules of use most often entails the appearance of incorrect indicators.
When diagnosing pregnancy, the test is used at the time indicated by the manufacturer. If testing is recommended from the first days of the delay, then it is likely that the sensitivity of the reagent or individual characteristics, the time of conception will reveal a pregnancy earlier than the specified period, but most often an accurate result is possible only on the specified days of the cycle.
The cost of the test most often directly correlates with its reliability: the lower the price, the lower the cost of production and the cheaper the chemical reagent, respectively, the higher the number of incorrect results. The tests of four modifications are the most common on the market today, each variety has its own characteristics and instructions for use. Some manufacturers produce various types of tests under a single brand (Evitest or Evitest, Frautest, etc.), when buying, you need to pay attention to the variety.
Test strip or strip test
The strip test (stripe test, strip test) is one of the first diagnostic options for pregnancy, a test for independent use and quick interpretation of the results. The most common and cheapest option (for example, Itest Plus is offered at a price of 20 rubles.).
A paper-plastic strip with an additional inner layer saturated with reagents, when exposed to urine, is painted in one or two places. One bar confirms the effectiveness of the test, two indicate the presence of a sufficient concentration of the hormone human chorionic gonadotropin to confirm pregnancy.
Rules of use: to collect the first morning urine in a clean container, lower the test to the border indicated on the strip, hold in the liquid for the necessary time (most often 20-30 seconds), remove and lay on a dry horizontal surface.
Diagnostic results appear over a period of 1 to 10 minutes, depending on the concentration of the hormone. Some tests can also change the degree of color of the control strip - the paler the color, the shorter the gestation period.
Tablet tests are based on the same principle of operation as strip tests: when a certain part of the surface comes in contact with urine, a chemical reaction of the reagent and the hCG hormone takes place. For a lesser likelihood of error, the volume of liquid is dosed, and the contact point is limited to a special window.
According to the instructions, urine must be collected in the supplied clean container, then using a pipette from the kit, dose 4 drops into a small window of the test tablet. The results are evaluated in the following window: depending on the variety, one or two strips or minus and plus appear.
This variety is considered one of the most accurate and sensitive, and also does not require additional devices and manipulations. A strip of dough is placed under a stream of urine for 10 seconds (if necessary, you can use the container and immerse the test in urine).
Results must be evaluated at intervals of 1 to 10 minutes, depending on the concentration of the hormone. In contrast to the above options, inkjet tests can be applied 5 days before the expected date of the onset of menstruation.
Digital Pregnancy Test
Electronic modification of conventional options. The test evaluates the concentration of the hCG hormone and requires immersion in the urine, but the result (depending on the type of test) is displayed either on an electronic mini-board or appears on the computer screen to which the test is connected via a USB port.
This option is considered the most optimal due to the impossibility of distorting the interpretation of the results. However, the sensitivity for digital tests is the same as for inkjet tests: they can be used 3-4 days before the expected date of menstruation. When testing 2 days before the start of menstruation, an accuracy of 99% is guaranteed.
Negative test result in developing pregnancy
In most cases, tests show a negative result in pregnant women with too early tests with low sensitivity, non-compliance with instructions for use or storage. A negative result is also possible due to late ovulation and late conception - in such cases, the hormonal background changes more slowly than expected in accordance with the menstrual cycle.
Diseases of the endocrine system, hormonal disorders also lead to the appearance of negative results in test diagnostics. An increase in the level of hCG hormone is inappropriate for the threat of miscarriage, which, accordingly, leads to one strip on the test at a time when the concentration of hCG should be sufficient for two.
It is worth knowing that during gestation, you can use tests only in the first trimester. The concentration of hCG is not maintained during the period of expectation of the child, which leads to incidents: if you conduct tests for a period of more than 2-3 months, the result will be negative.
False positive results
Positive test results in non-pregnant women are much less common than the reverse situation and in most cases indicate the presence of diseases (ovarian dysfunction, the formation of a tumor in the reproductive organs that produce hormones, etc.). False positive diagnostic results are also noted in the first two months of the postpartum period and when applying the test with an expired shelf life.
In some women, pregnancy is accompanied by menstrual-like discharge, similar in profusion, timing and manifestations to regular menstruation. As a rule, the discharge ends in the first trimester, however, there are known cases of their manifestations throughout the gestation period. In such situations, it is recommended to resort to blood test diagnostics, however, the use of tests is also possible.
Any test is based on assessing the concentration of the hormone in the urine and getting menstrual flow into it does not affect the effectiveness of the tests.
If the test results are in doubt
Sometimes it is not easy to interpret the results of express diagnostics: the second indicator strip is slightly outlined, it is visible from the inside of the test. Sometimes this happens due to poor-quality production of cheap paper test strips: when wet, the reagent becomes somewhat more noticeable than in dry form.
A visible, but pale second strip most often indicates a low level of hCG, insufficient for the sensitivity of the test. In this case, it is better to postpone the check for 1-2 days or use the more highly sensitive option.
A strip with an insufficient degree of staining can also occur as a result of improper storage of the test, violation of the instructions. In any case, repeated testing and / or a blood test for hCG is recommended.
Ectopic or non-developing pregnancy
The test results for ectopic and / or non-developing pregnancy are also positive: on the days of the alleged menstruation, the presence of a second strip on the test is most often noted. But an increase in the hormone level does not occur in such conditions; on repeated testing, the pregnancy indicator strip may fade or not appear, which requires immediate medical attention.
Until the 1960s, a pregnancy test was conducted only in the laboratory. In 1967, Margaret Crane, a 26-year-old graphic designer at Organon, an American pharmaceutical company, created the Predictor portable and easy-to-use test kit (retail), intended for retail sale. Its leaders did not approve of the invention, but reported it to the parent organization Akzo in Holland, where they became interested in the invention. In 1968, she personally presented the invention, coming without an invitation to a meeting at Organon on a home pregnancy test, and it was chosen from several options presented by different people. In 1969, Organon registered a patent with the name Margaret Crane in the column "inventor", and Margaret herself received $ 1 for the invention and information about the inventor was not published anywhere. Much later, in 2012, Margaret put up for auction the first sample of the test kit, which was stored at her home, and it was bought by the Russian Museum of American History. Smithsonian Institution, after which Margaret became known to the public.
The test predictor went on sale in Canada in 1971, while in the USA the approval was delayed for 5 years. In the first four years, revenue from sales of the test in the United States amounted to $ 40 million, the inventor did not receive anything.
Accuracy [edit |
Pregnancy test: principle of action
All pregnancy tests that exist today have the same principle of action: tests respond to the presence of the hCG hormone in the woman’s body.
The hCG hormone (its full name is human chorionic gonadotropin) begins to enter the woman’s blood from the moment the embryo is attached to the uterine wall, i.e. already on the 7th day from the moment of fertilization.
How to conduct a pregnancy test so that the result is as accurate as possible
The new generation pregnancy tests we use today have very high level of accuracy - 95-99%, however, a small fraction of errors remains.
Pregnancy test may show a false negative result in the following cases:
- you chose a test with low sensitivity and ran the test too early, before the hCG level had risen enough for the test to respond to it,
- on the eve of the test, you drank a lot of water - in this case, the urine is "diluted" and the concentration of hCG in it is reduced,
- You used an expired test or used it incorrectly.
In rare cases test result may be false positive:
- if fragments of the ovum remain in the uterus after a miscarriage or premature birth, the level of hCG may remain high, the test in this case will show a false positive result
- HCG is present in some infertility drugs (usually these drugs are injected)
- Unfortunately, an increase in the level of hCG can be accompanied not only by pregnancy, but also by malignant neoplasms.
Different tests have different sensitivity to hCG levels. The sensitivity of the test in units of mMU / ml (international units per ml) is indicated on the package. Depending on the level of sensitivity, the period varies during which the test can reliably show the onset of pregnancy:
- with a sensitivity of 20-25 mMU / ml - from the first day of menstruation,
- with a sensitivity of 10 mMU / ml - from 7-10 days from the expected date of conception.
Times of Day
Morning urine, namely its first portion, is the most concentrated, the level of hCG in it is as high as possible, therefore, if you plan to use a regular test, it is best to do this right after waking up. But if you have a highly sensitive inkjet test in your hands (10 mMe / ml on the package) - feel free to use it at any time of the day.
How to read the test result correctly
Тесты на беременность разнообразны по дизайну и способу использования, но формат «выдачи» результата у них общий, классический: две полоски означают беременность, одна полоска – нет. Немного отличаются только электронные тесты, у них наличие беременности показывает индикатор «+», отрицательный результат, соответственно, будет выглядеть как «-».
Когда оценивать результаты теста?
The test results should be evaluated strictly according to the instructions: as a rule, waiting time for the result is from 3 to 5 minutes. You should not wait longer “for fidelity”: after 10 minutes, the result may be unreliable due to exposure to the indicator of sunlight and other environmental factors.
Pale second strip
With bated breath you wait for the treasured two stripes, but the second strip is much paler than the first? Do not worry, if the second strip nevertheless appeared, albeit weakly - this means that there is pregnancy.
However, the hCG level is still not too high, but it is growing every day - you can repeat the test after 3-4 days - and if the process proceeds normally, both strips will be clear and bright.
Can I reuse a pregnancy test?
You did the test very early, the result was negative, you waited several days and are ready to conduct the test again. And then the thought comes to your mind: is it better to save money on the dowry for the future baby and use that first, negative test?
No, it’s definitely not worth doing this: the test indicator has already reacted with urine. A second reaction, of course, will occur, but what kind of result the test will show is unpredictable, and you still will not get reliable information. And why do you need extra excitement and doubt?
What will the test show with an ectopic or dead pregnancy
Just as a normal pregnancy, an ectopic pregnancy is accompanied by an increase in the level of hCG: it is obvious that the test will show a reaction to this level, giving positive result. To exclude an ectopic pregnancy, you can visit a gynecologist and have an ultrasound scan to make sure that the fetal egg is in the uterus.
As for a frozen pregnancy: when pregnancy occurs, the level of hCG grows at a normal pace, and from the moment of fading begins to fall. Depending on at what point you did the test, the result may be positive, even if the pregnancy has already stopped at that moment - after all, the level of hCG remains high for some time.