The pregnancy test of pharmacy, also known as homemade pregnancy test, has been on the market since the 1970s and has become increasingly reliable for the diagnosis of pregnancy.
All pregnancy tests act by detecting a hormone called human chorionic gonadotrophin (hCG), which is only produced when the woman is pregnant. Circumstances in which there is circulating hCG in the body are rare, without ongoing gestation.
The human chorionic gonadotropin hormone begins to be produced when the egg fertilized by a sperm is implanted in the uterus. This implantation usually occurs about six days after the sperm and egg meet. As pregnancy progresses, more hCG is produced by the fetus. In the first weeks of gestation hCG levels double every 2 or 3 days.
Pharmacy pregnancy testing is a good option for pregnancy screening, but the most reliable and definitive method for diagnosing pregnancy is the blood dosage of hCG.
Like any hormone, the circulating hCG in the blood is filtered in the kidneys and ends up being partly eliminated in the urine. Home pregnancy tests are based on the detection of hCG in the urine. The logic is simple if there is hCG in the urine is because the woman is pregnant.
Most current home pregnancy tests can detect the presence of hCG in the urine as early as the first day of menstrual delay. However, the amount of hormone in the urine at such an early stage of pregnancy may be small, leading to a dubious result (I explain later). Therefore, it is safest to perform the test after a week of delayed menstruation.
If you think you may be pregnant but your first test was negative, repeat it after one week. In this short time the concentration of hCG reaches quadruple, reducing the risk of a false negative result.
There are dozens of different types of pregnancy tests on the market. Some are of better quality than others, being able to detect very small levels of hCG in the urine. However, after a week of menstrual delay, the amount of urinary hCG is already high enough that all pharmacy tests can detect the presence of the hormone.
As already said, there are dozens of different home pregnancy tests. Let's use a dummy model to explain how the test should be done. Usually the tests are all very similar. Use this text as a guide, but be sure to read the package leaflet you have purchased before using it.
1. Only open the test at the time you use it and only after you have read the test instructions. You do not need to use the first urine in the morning. The test can be done any time of day.
2. Remove the test cap to expose the absorbent strip.
3. Urinate at the absorbent tip for 5 to 10 seconds so that it is well moist. One option is to urinate in a small container and then dunk the tape for 3 to 5 seconds.
4. Replace the absorbent tape and rest the test on a bench.
5. The result starts appearing after 1 minute.
How to interpret the result of the homemade pregnancy test?
Every home pregnancy test has two small windows, one that is called a control window and another that is the result window. All tests have a clear indication of which.
As soon as the tape comes in contact with the urine, a risk appears in the control window to prove that the amount of urine was sufficient. If a risk does not appear in the control window, the exam is not valid.
In the image below we show four examples of results of the pharmacy pregnancy test. The control window is the top window and the result window is the bottom window.
One minute after the urine has come in contact with the test, if there is hCG in the patient's urine, ie if the patient is pregnant, the outcome window begins to present a similar risk to that of the control window. The higher the hCG level, the stronger the line. If the test is done at a very early stage of pregnancy, the line that appears in the result window can be very tenuous, difficult to identify.
When the woman is not pregnant the result window does not change and is "blank". The tape only reacts if there is hCG in the urine.
It is important to point out that in the negative exam no line appears. If a line appears, even if very weak, the test should be interpreted as possibly positive. In this case, the patient may choose to repeat the pharmacy test after two or three days to see if the line gets more intense. Taking the blood test is another option, since it is more sensitive and stays positive before the urine test.
Most pharmacy exams should have your result read with an interval of 1 to 10 minutes after its completion. The test should not be read too long since after urine evaporation, a line may appear in the result window, without this meaning the presence of hCG. Therefore, if no lines appear in the result window after 5 to 10 minutes, the test is negative.
False positive and false negative result of the pharmacy pregnancy test
