How does a pregnancy test work?
Technically, a pharmacy pregnancy test is simple. It is a reagent applied to paper that reacts to a specific substance – a hormone called human chorionic gonadotropin (hCG). When the hormone interacts with the test reagent, a specific color appears – a second stripe.
This hormone begins to be produced in a woman’s body only after the fertilized egg attaches to the lining of the uterus (endometrium). Typically this happens after about 6 days after fertilization. HCG is detected in blood and urine. When pregnancy occurs, its level approximately doubles every 48-72 hours.
Already by 10–14 days after conception, home pregnancy tests detect the hormone in the urine and report this by highlighting the second strip or the corresponding window on the indicator.
If you see two stripes or a plus sign on the indicator, it means pregnancy has occurred. Error is practically eliminated. It is important to remember that a pregnancy test shows the presence of any pregnancy: both uterine (normal) and ectopic, that is, ectopic.
Can a pregnancy test be wrong?
Sometimes yes. The likelihood of this depends on various factors, including the result obtained.
When a pregnancy test can be false positive
Situations when a woman is not pregnant, but the test shows two lines, are extremely rare.
That’s why countsthat a positive result is almost always true.
However, it’s worth knowing causes, for which the test may be false positive. Spoiler: many of them require mandatory consultation with a gynecologist, so if you see two stripes or a plus sign on the indicator, visit your doctor It’s better not to delay.
- You lost your pregnancy shortly after the egg attached to the lining of the uterus, that is, a biochemical pregnancy occurred. In this case, the embryo no longer develops and technically you are not pregnant, but within 2-3 weeks the test may still detect elevated hCG levels. Most often, the fertilized egg is rejected and comes out with the onset of menstruation. Sometimes with a biochemical pregnancy, a woman may not even know that she was pregnant;
- You took the test shortly after using hCG products. After using these drugs, hCG can remain in the body for 10-14 days after the last use;
- You develop a hCG-producing tumor (chorionepithelioma or hydatidiform mole);
- Your test is of poor quality or the rules for its storage and use have been violated.
When a pregnancy test can be false negative
A false negative result is when pregnancy has occurred, but the test for some reason does not show it. This situation is more common. Therefore, doctors recommend repeating the test after a few days if signs of pregnancy (for example, delayed menstruation, enlarged and painful mammary glands, nausea) persist.
Here are the most common ones causes false negative result.
- You purchased an expired or damaged test;
- You took the test too early. And the level of hCG in the urine has not yet risen high enough for the reagents to detect it. Most manufacturers recommend taking the test no earlier than the first day of your missed period;
- You hurried, checking the result. It takes time for the reagent to catch the hCG and for the second strip to appear. It is usually indicated in the instructions. For example, the manufacturer may say, “Dip the test strip into the urine, hold for 10 seconds, then place on a dry, horizontal surface. The result will appear in 4-7 minutes.” If you check the test before 4 minutes, you risk seeing a false negative result;
- You took the test in the evening. The vast majority of manufacturers recommend checking if you are pregnant in the morning. This is important because in the morning urine is the most concentrated, and the level of hCG in it is the highest. By the evening in the earliest stages of pregnancy, the test strip may be false negative;
- Before taking the test, you drank a lot of water or other drinks (tea, juice, compote, fruit drink). The liquid dilutes the urine and reduces the concentration of hCG.
What to do if you think the pregnancy test is wrong
Several options are possible. Choose any one or try them all one by one.
Double-check the result
Repeat the test the next morning. Or, better yet, in 2-3 days.
When purchasing a second, screening test, ask the pharmacist at the pharmacy to give you the most sensitive one available. The sensitivity is indicated on the package and is indicated by numbers – 10, 20, 25, 30. These numbers indicate the concentration of hCG in the urine (in mIU/ml) that the test is capable of detecting. The lower the number, the more sensitive the test is.
Take a blood test for hCG
This is a more accurate and reliable option than urinary rapid pregnancy tests. A blood test can detect pregnancy within 6–8 days after conception – that is, even before a delay occurs.
Consult a gynecologist
Sometimes it happens that the test results do not correspond to how you feel. For example, your period is already delayed by several days, but the test stubbornly shows “no pregnancy.”
Various malfunctions in the body’s functioning, such as diseases, often lead to questionable results thyroid gland, disturbances in the production of female or male sex hormones, ovarian cysts. To rule them out, a visit to the doctor is needed.
The gynecologist will ask you about your symptoms, conduct an examination, offer tests or an ultrasound examination of the pelvic organs, and find out exactly why rapid pregnancy tests give ambiguous results. If any disease is discovered, the doctor will tell you how to treat it or refer you to a specialized specialist.
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