Pregnancy test: how it is done

One of the most frequent questions we receive from our readers is how to perform the pregnancy test to achieve a reliable result.

In the absence of menstruation, the most important pregnancy symptom, or any other symptom, many women want to confirm the suspicion by a pregnancy test, a method that allows, with a high margin of safety, to know if she is pregnant or not.

Types of pregnancy tests: blood and urine tests

There are two types of pregnancy tests: blood and urine. In both, the presence of the hormone human chorionic gonadotropin (hCG) is detected, also known as pregnancy hormone. This begins to occur after the implantation of the embryo and remains at high levels during the first trimester of pregnancy, although after that period drops, so if you performed a pregnancy test after the first trimester could be negative.

The blood test is performed in a laboratory and can detect pregnancy even before the first lack of menstruation. Quantitative tests can detect hCG levels as small as 1 mIU/mL, while urine tests require 20 to 100 mIU/mL, depending on the brand. A precise result can be obtained in a few hours, including determining the exact age of the fetus, as well as detecting abnormal pregnancies such as an ectopic pregnancy, a molar pregnancy or a potential miscarriage.

The urine test can be purchased at the pharmacy without a prescription to be made at home. It consists of an absorbent strip, normally presented inside a plastic cartridge, which reacts to the presence of the hormone human chorionic gonadotropin in the urine.

They have a reliability between 75 and 97 percent if the result is negative, while if the result is positive the reliability is 99 percent.

There are more sensitive than others, according to the brand. Try to buy the ones that detect the lowest concentration of hCG. For example, a test that claims to detect hCG at 20 mIU / ml (International MilliUnits per milliliter of urine) will be more sensitive than one that claims to detect it at 50 mIU / ml.

How the pregnancy test is performed

The blood test is performed in a laboratory by extracting a sample of blood from the woman. It does not require fasting and can be done at any time of the day.

The urine test is done at home. The first thing you should do when opening the test is to read the instructions in the attached brochure since the way to do it can vary from one brand to another. Although it can be done at any time of the day, for greater reliability it is recommended to do it with the first urine in the morning, to ensure that there will be more concentration of the hormone.

If you follow the manufacturer’s instructions, you will see that the procedure is very simple and practically does not give rise to errors. You must unwrap the test, remove the lid of the test strip and place it for 5 seconds in direct contact with the urine while you pee. Once the urine is collected, you must recap the test (it is important not to come in contact with any other substance), place it on a flat surface and wait for 3 to 5 minutes to read the result.

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The result of the urine test

Each brand has a different result reading system. The most common is that of the two lines for positive, even if they are faint. One of them indicates if the test has been done well and the other indicates the presence of the pregnancy hormone in blood. Therefore, the presence of a single line indicates that the test has been done well and the result is negative.

Some tests, instead of the system of stripes or symbols, incorporate a small digital screen in which the result and the weeks of gestation are indicated. In any of them, if no result appears, it is most likely that the test is poorly performed, so the test must be repeated.

False negatives and false positives

The result may be negative when you are actually pregnant. This may be because you have done the test too early for the concentration of the pregnancy hormone to be detected in the urine. If the rule still does not come you should repeat the test a few days later or a week.

The false positive result, that is to say that the test yields a positive result when you are not pregnant, is very rare. It may be due to having suffered a spontaneous or voluntary abortion in the last eight weeks, having taken a medication to increase fertility that contains hCG, having an ectopic pregnancy (produced outside the uterus) or an anembryonic pregnancy (there is no embryo present). These circumstances can increase the level of human chorionic gonadotropin hormone even without having a real gestation.

We hope we have clarified what a pregnancy test is and how it is performed. In a next post we will talk about when to perform the pregnancy test, also a very frequent concern when the possibility of pregnancy arises.

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