What is a pregnancy test and how does it work?

Pregnancy tests detect the presence of human chorionic gonadotropin (hCG) in a woman's urine or blood. This hormone begins to be actively produced by the membranes of the embryo 6-8 days after fertilization. It is during this time that the egg penetrates the walls of the uterus. In a non-pregnant woman, the normal level of the hormone is below 5 mIU/ml and tests do not respond to it. As soon as a woman begins to bear the future fetus, the concentration of the substance begins to increase sharply, to which tests respond with a positive result.

Operating principle of the tester

Testers of the new generation have become a common occurrence in life. Their function is based on the simplest principle of diagnosing the hormone human chorionic gonadotropin in the urine of the intended mother.

This substance is found in every human body at a level from 0 to 5 mIU/ml. But after fertilization, the concentration of hCG in female cells increases, and by 1–2 weeks it already exceeds the initial level by more than 5 times (sometimes 20 times).

An increase in gonadotropin levels at this moment is diagnosed by a test in the form of two colored stripes or other values.

Pregnancy indicator strips contain antibodies that recognize hCG and stain under its influence. One strip is always painted, this is simply an indicator of the suitability of the device for use. And the second changes its color only under the influence of contact with human chorionic gonadotropin. This means that if the test shows two lines, the answer is affirmative: pregnancy. If only one marker appears, the answer is negative.

What types of pregnancy tests are available?

There are 2 main types of pregnancy tests: urine and blood tests. Urine testing is the most practical and convenient because it can be performed at home. In pharmacy chains and on supermarket shelves you can see a wide variety of testers in different price categories. They differ in their level of sensitivity to hCG.

The more expensive ones react to relatively low levels of increased hormone levels (10 mIU/ml), and, therefore, make it possible to clarify the fact of motherhood at an earlier date - 7 days after conception (5 days before the delay). You should expect a positive result from cheaper testers from 1-3 days of missed period, when the concentration of the hormone in the urine is at least 25 mIU/ml.

Pregnancy tests also differ in how they are used:

test strips. They are the most popular option to use. They are impregnated with special reagents that perceive hCG. They must be lowered into a container with urine to a certain mark and wait a few seconds. You should expect results within 5 minutes, but not later than 10;
inkjet tests. There is no need to collect urine to perform it. It is enough to hold it under a stream of urine for a few seconds and wait for the result;
tablet test. This option is a strip placed in a plastic tablet with two windows. A small amount of urine is placed into one of them using a pipette. The result will be visible in the next window in a few minutes;
electronic test. It is the most accurate of all the previous ones. The principle of its operation is similar, but the result is displayed on the screen.

What affects the readings?

First of all, timing can affect the accuracy of the test system. If a woman is in a hurry and does not comply with the optimal testing times indicated above, then the likelihood of getting an unreliable result increases significantly. Even high-precision digital tests 4-5 days before the onset of a delay determine pregnancy, according to manufacturers, with only a 50% probability, but already 1-2 days before the onset of a delay, the predicted accuracy exceeds 90%

Therefore, it is very important to adhere to the deadlines, understanding that hCG cannot appear in the urine the day after conception in principle. And if it can, it’s clearly not because of pregnancy.

A woman may receive unreliable results due to the presence of neoplasms in the body, tumors that themselves produce hormones. Most often these are malignant tumors. In this case, even outside pregnancy, the level of hCG will be elevated, and tests may give a positive result.

If a woman underwent hormonal testing in the current cycle, or conception occurred as a result, you should also not count on the accuracy of the test systems. When treating infertility using these methods, the drug hCG is administered to speed up the maturation of eggs, and traces of the hormone are still detected in the urine and blood for at least 10–13 days. The test in this case can also show a second line without good reason (that is, without the fact of pregnancy as such).

One of the most common reasons for receiving false results is violation of self-diagnosis rules. Manufacturers provide each system with instructions for use. It cannot be violated. For example, strip strips cannot be immersed deeper into urine than is suggested by drawing a line with the MAX mark. After soaking, they cannot be kept for longer than the time allotted for diagnosis. If a negative test is left for half an hour, a second pale grayish stripe may appear on it, and this will not be a sign of pregnancy, but simply traces of dried applied reagent.

Jet tests must be held under stream of urine for 5-10 seconds, they are not immersed in a container with urine. Tablet tests involve instilling urine with a pipette into a special window with a test zone, while digital tests can be carried out using either the jet method or with preliminary urine collection.

The test should not be expired or faulty, and therefore the expiration dates should be examined and the integrity of the packaging should be visually assessed. You need to buy such products at a pharmacy, and not at the checkout counter of large supermarkets, because in the second case there is a higher risk of getting a faulty product, since the storage conditions in the store may not meet the manufacturer’s requirements.

Is it difficult to take a pregnancy test at home?

Carrying out the test at home does not present any difficulties. It can be purchased at any pharmacy without a prescription or in a supermarket. In addition to their accessibility, the tests are highly accurate. The main task when performing them is to strictly adhere to the instructions. The correct result should be expected after the time interval indicated in the instructions. A result that appears earlier or later than the specified time is not correct. If a woman has doubts about the reliability of the result, it is better to contact a gynecologist.

When is the right time to take the test?

The earliest time for diagnosis is 8 days after the expected conception. At this point, you can only use a laboratory blood test, since all other methods will probably give an inaccurate result.

As for the pharmacy test, it is used a little later:

1-2 days after a missed period;
2 weeks after the expected conception.

However, it is not recommended to rush. The strips are most accurate 7 days after the delay. It is at this time that you can find out the correct result with a probability close to 100%.

How accurate are pregnancy tests?

Home tests do not provide a complete guarantee of obtaining a reliable result; mistakes sometimes occur. To achieve more accurate data and minimize possible errors, the following rules must be followed:

It is advisable to carry out pregnancy tests in the morning, since the largest amount of the hormone is concentrated in the urine overnight;
Before conducting a urine test, the test should not be exposed to dirt or moisture;
It is unacceptable to use the test after the expiration date;
foreign substances should not penetrate into the urine sample;
the test kit should be stored at a temperature of 2 to 28C;
When performing the test, you must strictly follow the instructions.

Blood test for hCG

In addition to home tests, doctors recommend taking a blood test. It is more informative, since the concentration of the hormone in the blood is several times higher than in the urine. The test can detect pregnancy earlier than urine tests, but it takes longer to complete.

There are 2 main types of blood tests for hCG:

qualitative. Answers the question: is the hormone level elevated or not, which indirectly suggests the presence or absence of pregnancy in a woman;
quantitative (beta-hCG). This analysis reflects the exact concentration of the substance in the blood, so the doctor can monitor hormonal changes over time.

To obtain correct blood test results, you must adhere to the following rules:

the analysis is performed strictly on an empty stomach in the morning;
12 hours before the test, alcohol consumption, physical activity, and smoking should be completely avoided;
In the morning on the day of analysis, drinking water is allowed;
It is necessary to avoid taking any medications. If this is not possible, you need to notify the laboratory and doctor.

Determining pregnancy is not the only task of a blood test for hCG. As noted earlier, during the formation and development of the embryo, the level of the hormone in a woman’s body should gradually increase - up to the 12-13th week of pregnancy. If, with regular observation, an increase in hCG is not observed or the hormone level does not correspond to generally accepted standard values for a specific period, then this may indicate the development of a frozen or ectopic pregnancy, with a high probability of miscarriage.

At later stages, quantitative determination of hCG can be used as a screening for genetic disorders in the fetus (Down or Edwards syndrome). The determination of beta-hCG also plays an important role. If a woman’s level of this hormone is elevated, but other characteristic signs of pregnancy are not observed, tumor diseases should be suspected.