2023 Author: Anita Thornton | [email protected]. Last modified: 2023-05-22 03:30
The reliability rate of pregnancy tests is very high. However, it happens, although rarely, that the results are erroneous. We then speak of “false-positives” or “false-negatives”. But what can falsify a pregnancy test? Let's explore the subject!
A result will be said to be a “false negative” if it indicates that you are not pregnant even if fertilization has taken place. It also happens, although it is much less common, that a test reveals that you are pregnant, when you are not. This is a “false positive”.
On the reliability of pregnancy tests
As soon as the embryo implants itself in the wall of the uterus, the placenta forms and begins to produce a hormone, human chorionic gonadotropic hormone (HCG), which will be found in the blood, but also in the urine of the pregnant woman.
The pregnancy tests you buy at the pharmacy are urine tests; they have a reliability of between 98 and 99%. If they are almost all the same, some are more sensitive than others and will be able to detect HCG more quickly, even if the hormone isfound in lower concentrations. Thus, the most reliable tests manage to detect 40 to 50 IU of hormones per litre. These tests allow a positive result more quickly than the others.
Indeed, most pregnancy tests will detect HCG from the day your next period is due – so from when your period is late.
Wondering when to take the pregnancy test?
Although tests now allow you to detect the hormone a few days before your expected period, experts agree that the best time to take a pregnancy test would be one to two weeks after the expected date of the next period. The result will then be much more frank, surer.
Negative Pregnancy Test: False Negatives
False negatives are most often the result of misuse of the pregnancy test: for example, when you take the pregnancy test too soon, or when the expiry date of the test has passed.
If you have an irregular cycle, it is possible that the theoretical fertilization date does not correspond to your calculations. The more concentrated the urine, the more reliable the test result will be: morning urine contains more HCG. So if you drank a lot of fluids before taking your test, your urine may be toodiluted.
Rarely, it should be noted that abnormal bladder or kidney function can also lead to a false negative result. In any case, if you still think you are pregnant, wait a few days, and take another test.
“Two pharmacists to whom I had shown the result of my stick test, containing a light line and a dark line, (a double bar, and another very pale, even invisible) had confirmed to me that I wasn't pregnant, while I was. Can you believe: one of them almost bet his career! If only he knew, poor thing! My friend also had a supposedly negative pregnancy test, then a period-like bloody discharge in the first month. Imagine her surprise, on the ultrasound, to learn that she was a month older than she really thought! – Caroline
Positive Pregnancy Test: False Positives
Much less frequent than false negatives, false positives are still possible. This happens when you receive a positive pregnancy test but you are not pregnant.
They are usually observed very early in pregnancy during a miscarriage, or after taking certain medications, especially those used in the infertility treatment.
The presence of an ovarian cyst could also distort the results, as well as abnormal bladder or kidney function.
“I was a few days late, and I took a test: positive!To be sure, and not to create false joy, I spent another. This time the result was negative. My boyfriend went to the pharmacy, and I took three more tests: all negative. When calling the clinic, I was told that false positives were virtually impossible, and I was invited to take a blood test, which was said to be 100% reliable. It turned out negative. We have to take it on the bright side: nothing is impossible! – Karine