Pregnancy test results
A pregnancy test is an early diagnostic method based on the detection of specific hormonal markers in a woman's urine. The main such marker is human chorionic gonadotropin or hCG for short. Rapid testing, thanks to compact and convenient devices, can be performed at home, which is used by millions of women around the world.
HCG is a special pregnancy hormone that is produced by the cells of the membrane that covers the embryo. It is called "chorion". Chorionic gonadotropin is present in the serum of both men and non-pregnant women, but its amount does not exceed 5 IU / ml. After conception occurs, the hCG level rises sharply. By the end of the first week, it reaches 25-300 IU / ml and will continue to increase further. If, according to a blood test, pregnancy can be detected as early as 6-10 days after fertilization of the egg, then the required concentration of the hormone in the urine most often reaches its values by 10-15 days. Although some test manufacturers claim that with the help of their devices it is possible to determine pregnancy even 7 days after conception.
There are several types of express tests on the market that allow you to diagnose pregnancy at home.
All of them have different sensitivity to chorionic gonadotropin, ranging from 10 mIU / ml and ending with 25 mIU / ml. Among the test systems are:
- Strip tests or test strips that have been impregnated with the reagent. It is an antibodies to chorionic gonadotropin that react with it and stain the indicator in a bright color. A portion of urine is required for the study. If it contains a high level of hCG, then two stripes will appear on the test, which indicates pregnancy. If there is no pregnancy, then there will be one strip.
- Tablet tests are a paper strip that is enclosed in a plastic box. It has two windows. A few drops of urine are introduced into one of them with a pipette. The liquid reaches the reagent applied in a thin layer, and if hCG is present in the urine, the test result will be positive. It appears in the second window and is represented by two stripes. If there is no pregnancy, then only one band will appear - the control one. It is necessary in order to understand that the test is not defective and worked correctly.
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The inkjet pregnancy test differs from its "counterparts" in the form and method of use. The system itself is represented by an elongated plastic cassette, which has a holder and a tip covered with a cap. To conduct the study, the tip from the cap is released and brought under the stream of urine. Through the fibrous rod, which has tubules, urine rises up and reaches the reagent. If hCG is present in the urine, then the test produces two strips (positive result). If the level of hCG in urine is low, then the test produces 1 strip (negative result).
- Electronic tests operate on the principle of jet tests, but the answer is displayed on a digital display with which the device is equipped. Moreover, the result is manifested in the words "pregnant" or "not pregnant", or in the signs "+" and "-". Such devices can additionally indicate the gestational age and even recommend the optimal date of conception if it has not yet occurred. Some modern pregnancy tests connect to a computer via a USB port and display all the information on a monitor.
The most sensitive tests are inkjet devices, with or without an electronic display, and tablet tests.
Content:
- Why is a pregnancy test positive?
- Why is a pregnancy test negative?
- When is a pregnancy test false positive?
- Will the test show a frozen pregnancy?
Why is a pregnancy test positive?
If the pregnancy test shows a positive result, it means that it has interacted with the hCG hormone in the urine, and the woman is pregnant. This is the most obvious reason why a pregnancy test is positive. However, there are exceptions to any rule. Sometimes it happens that the test is positive, and the woman has no pregnancy. In this case, we can talk about a false positive pregnancy test result. The reasons for receiving it will be indicated below.
Why is a pregnancy test negative?
If the pregnancy test is negative, then the woman is not pregnant. However, as with a positive pregnancy test, things are not so straightforward.
It is possible that the test gives a false negative result, which can be obtained for a number of reasons:
- The test was done too early. Sometimes a woman, in an effort to quickly find out the result, rushes to conduct a study. In this case, the answer may be negative, not because there is no pregnancy, but as a result of a low level of hCG in the urine. Another situation in which testing is carried out too early is due to the fact that the woman has an unstable menstruation schedule. In her opinion, she is conducting research on the first day of the delay in menstruation, and it has not yet come. And conception itself could have occurred not in the middle of the cycle, but at its end. Therefore, hCG by the first day of delay in menstruation does not reach the level that could be determined using a pregnancy test.
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The test can give a negative result in the actual presence of pregnancy when the urine is highly diluted. This can happen if the woman consumed a large amount of liquid throughout the day and performed the study in the evening. A decrease in the concentration of hCG in the urine is facilitated by the intake of diuretics. Therefore, doctors recommend conducting the study in the morning, using the first portion of urine for testing.
- If a woman has an ectopic or frozen pregnancy, then the test may show a negative result for a long time. The fact is that in pathological pregnancy, hCG is produced, but in smaller volumes than with a normally developing pregnancy. As a result, the test will still show two stripes, but this will not happen in the early stages.
- Against the background of diseases of the urinary system, the test result may be negative even with an existing pregnancy, since hCG will not be excreted from the body in the proper volumes due to impaired renal function.
You should also not exclude such reasons for obtaining a false negative test result, such as device breakdown, improper storage, or expired shelf life. While the main reason a pregnancy test is negative is the absence of pregnancy.
When is a pregnancy test false positive?
Sometimes it happens that a pregnancy test shows a false positive result.
This can happen for a number of reasons, for example:
- A woman has a trophoblastic neoplasm in her body that produces the hCG hormone (chorionepithelioma, chorionic carcinoma). Or it can be a tumor of the ovaries, uterine fibroids, etc.
- A false positive test result is also observed if the treated tumor recurs.
- Cancers such as colon cancer, stomach cancer, kidney cancer, and lung cancer can lead to a false positive result.
- With brain tumors or with brain injuries, chorionic gonadotropin can be produced in excess amounts in the pituitary gland.
- Another reason for a false positive pregnancy test is cystic drift. It also belongs to the group of trophoblastic diseases and is characterized by the transformation of the villi of the outer shell of the embryo into cysts.
- The expiration date of the test has already expired or the woman has acquired an unusable device. Sometimes tests are simply defective or stored incorrectly. Therefore, before buying, be sure to check the expiration date of the test. It will not be superfluous to ask the pharmacist for a certificate for the device. The integrity of the package in which the test is located must not be broken.
- During the study, the woman departed from the instructions. It is possible that the test has been exposed to urine for too long or too little. It is possible that the result was assessed later than the time indicated in the instructions for use, etc. In order to minimize the risk of obtaining a positive result in the absence of pregnancy, it is necessary to strictly follow the instructions. It is attached to each device and defines a strict sequence of actions.
- The woman has recently had an abortion, miscarriage, or ectopic pregnancy. In each of the three listed cases, the level of hCG in the body will return to normal, on average, in a month. Therefore, during this time, the test result may be positive, despite the absence of an embryo in the uterine cavity.
- A woman takes medications that contain chorionic gonadotropin. They are used to treat infertility. It can be the drug Pregnyl, Profazi, Ovitrel, etc. The test in this case does not make sense to perform. Moreover, the result may be positive even after the completion of the therapeutic course, since the components of the drug are not immediately excreted from the body. This will take about two weeks.
Although there are many reasons why a test may show a false positive result, it is extremely rare for devices to make mistakes.
Will the test show a frozen pregnancy?
If a woman has a frozen pregnancy, then the test will show it. Most likely, the result of a pregnancy diagnosis will be positive, but it is impossible to determine with the help of a test what kind of pregnancy a woman has.
A positive test result is not a basis for making an assumption about how a woman's pregnancy develops - normally, or she froze. Only a doctor can help determine this issue.
As for why the test gives a positive result against the background of a frozen pregnancy, the answer lies on the surface. The fact is that hCG will continue to be produced by the embryonic membrane, even if the fetus itself has already died.
The author of the article: Lapikova Valentina Vladimirovna | Gynecologist, reproductologist
Education: Diploma in Obstetrics and Gynecology received at the Russian State Medical University of the Federal Agency for Healthcare and Social Development (2010). In 2013 completed postgraduate studies at N. N. N. I. Pirogova.
