Positive or negative? How reliable are pregnancy tests?

Pregnancy tests available today are over 99% reliable… provided they are used correctly! A pregnancy test can be bought in pharmacies, drugstores or supermarkets. “Tests bought in supermarkets are just as effective as those bought in pharmacies. However, by purchasing your test in a pharmacy, you will be able to benefit from the advice of a health professional ”, underlines Dr Damien Ghedin. If you need advice, therefore, buy your test from a community pharmacy.

How does a pregnancy test work?

To use a pregnancy test properly, you have to understand how it works! “A pregnancy test detects the presence or absence of a specific pregnancy hormone in the urine, the beta-HCG (hormone chorionique gonadotrope)» explains Dr. Ghedin. It is the placenta, more precisely the trophoblast cells, which will produce this hormone from the 7th day after fertilization. This can therefore only be physiologically present in the body during an ongoing pregnancy. Its concentration in the blood and urine will increase very quickly during the first 3 months of pregnancy. Indeed, its rate doubles every 2 days during the first 10 weeks of pregnancy. Its concentration then decreases during the 2nd and 3rd trimester of pregnancy. After childbirth, the hormone is no longer detectable.

When the urine stream comes in contact with the pregnancy test, an immunological reaction will occur if sufficient pregnancy hormone is present in the urine. Most tests are able to detect beta-HCG from 40-50 IU / liter (UI: international unit). Some tests, the early tests, have even better sensitivity and are able to detect the hormone from 25 IU / liter.

When to take a pregnancy test?

A pregnancy test will only be reliable if it is taken at a time of the day when sufficient pregnancy hormone is present in the urine. In principle, the tests can be carried out from the first day of late period, or even 3 days before for early tests! However, Dr Ghedin recommends not to hurry too much to take the pregnancy test: “For maximum reliability, wait until you have a few days late before taking your pregnancy test urinary”. If the test is done too early and the hormone concentration is still too low, the test could be false negative. The tests were designed to detect pregnancy based on a typical cycle: ovulation on day 14 and menstruation on day 28. Not all women ovulate exactly on day 14! Some ovulate later in the cycle. In the same woman, ovulation does not always take place on the exact same day of the cycle.

Are you several days late? The first thing to do is to read the instructions for each urine pregnancy test. The instructions may slightly depending on the model and depending on the brand of the test. Ideally, the test should be performed on the first morning urine, which are the most concentrated. “To avoid diluting the pregnancy hormone in a large volume of urine, you should also avoid drinking too much liquid (water, tea, herbal tea, etc.) just before taking your urine pregnancy test.“, Advises pharmacist Ghedin.

Reliability of early pregnancy tests: 25 IU?

Early pregnancy tests have better sensitivity, 25 IU according to the manufacturers! They can in principle be used 3 days before the expected date of the next period. Pharmacist Ghedin warns: “for many women, it remains difficult to assess with precision the theoretical day of arrival of their next period! It is recommended to wait a few days before performing the test in order to avoid any false negative “.

Can a pregnancy test be wrong?

Test negative and yet pregnant! Why ?

Yes it’s possible ! We speak of “false-negative”. However, this is a rather rare situation if the test is used correctly. If the test is negative while the woman is pregnant, it means that the test was carried out on urine that was not sufficiently concentrated in the pregnancy hormone. This increases rapidly at the start of a pregnancy. pharmacist Ghedin recommends: “If pregnancy is indeed possible and you want to be absolutely sure, repeat a test a few days later«.

Is it possible not to be pregnant if the test is positive?

Yes, it is also possible! With the tests available today, this is an even rarer situation than a “false negative”. If the pregnancy test results positive when the woman is not pregnant, this is referred to as a “false positive”. This is because the tests were designed to specifically detect a hormone that is only present in pregnancy. Nevertheless, the “false-positive” is possible in certain situations: in case of infertility treatment or in case of ovarian cysts. Finally, another cause is possible: early miscarriage. “The test is positive even though you are no longer pregnant“, Explains Dr Ghedin.

What about the reliability of homemade pregnancy tests?

How did our grandmothers know if a pregnancy was in progress? They were using homemade pregnancy tests! “The reliability of these tests is of course much lower than the tests available today. If you want to try, then take a urine pregnancy test bought at a pharmacy to be sure of the result.»Emphasizes the pharmacist.

However, these tests were based on the same principle: detecting the pregnancy hormone, beta-hcg, in the urine. For example, it was necessary pee in the evening in a glass and place it in the fridge all night. If the next day a whitish cloud had formed in the urine glass, it meant that the woman was certainly pregnant.

Another homemade pregnancy test involved peeing in a glass jar. After placing a new needle in it, it was necessary to close the jar well and place it in a dark place. If the needle blackened or started to rust within 8 hours, you might be pregnant!

As the pharmacist reminds us, “the women were also attentive to the symptoms heralding a pregnancy such as tense breasts, unusual fatigue, morning sickness … and of course a late period ! ».

What about online pregnancy tests?

It is possible to buy pregnancy tests online. First thing to remember: a urine pregnancy test is for single use only! So don’t buy never used pregnancy tests.

If you decide to buy your pregnancy test online, be careful about where the test came from and the seller’s reliability. The test must include CE marking, guarantee of the quality of the test. Pregnancy tests must meet the safety and performance criteria established by Directive 98/79 / EC relating to in vitro diagnostic medical devices. Without the CE mark, you should absolutely not trust the test results.

In the slightest doubt, the ideal is to go to the local pharmacist. Plus, if you’re in a hurry, you’ll save yourself the test delivery time.

What to do after a positive urine pregnancy test?

Urine pregnancy tests are reliable. However, to be 100% sure, you have to do another type of test: a blood pregnancy test. It’s a blood test. Here too, it is a question of beta-HCG dose no longer in the urine, but in the blood. While the urine test is not reimbursable, the blood test is reimbursed by Social Security on medical prescription.

To carry out this examination, you must go to a medical analysis laboratory, with a prescription from the attending physician, midwife or gynecologist. It is usually not necessary to make an appointment.

«Wait 4 to 5 weeks after the presumed fertilization date to take the blood test ”, recommends the pharmacist, there too to avoid any false negative. The blood test can be taken at any time of the day. It is not necessary to be on an empty stomach.

Now you know almost everything about the reliability of pregnancy tests! If you have the slightest question, do not hesitate to seek advice from a dispensary pharmacist, a midwife or your attending physician.

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