A pregnancy test is one of the most reliable methods to confirm if you are pregnant or not. Usually, a woman starts imagining that she could be pregnant when the period does not arrive when it was expected. In addition to this, she also experiences a higher sensitivity in her breasts, headaches, cramps, nausea, etc. After being aware of these symptoms, women decide to take a pregnancy test.
What is a pregnancy test
This tests measure the levels of the hCG hormone in blood, which is a key marker of pregnancy. However, this hormone cannot be detected until 14 days after the alleged day of conception. A pregnancy test should be taken by collecting a sample of urine, preferably the first urine after waking up.
The hCG hormone begins to gain presence thanks to the embryo, responsible of its spread from the sixth day of pregnancy until the second or third month of pregnancy, where the placenta starts secreting hormones on its own, so the levels of hCGdecrease until its presence in blood virtually disappears. The main role of this hormone is to maintain the corpus luteum during the beginning of pregnancy. It also intervenes in the immune tolerance during pregnancy, protecting the early fetus to get rejected by the mother’s immune system.
Since the presence of this hormone decreases as the pregnancy goes by, a pregnancy test taken during the second or third trimester could result negative, although it does not mean that the woman is pregnant, because her belly, the ultrasounds and the other symptoms will prove that she is.
Pregnancy tests in assisted reproduction
In a cycle of assisted reproduction, monitoring the ovulation cycle and working out the precise moment of fertilization are crucial during the whole procedure. Before transferring the embryos, doctors run analyses to detect the levels of the hCG hormone 15 days after the ovarian puncture. These analyses are blood analyses, which are more precise than urine analyses. If the concentration is above 10 IU/ml, the test can be considered as positive. However, when the results are around this threshold, it is required to make a regular follow-up of the hormone to rule out a biochemical pregnancy.
False negative pregnancy test
Many women experience the typical symptoms of pregnancy even before confirming it by a test. Some of these symptoms might be psychological or just PMS. Yet, there is a percentage of women who will get false negative results because it was too soon to take the test or because of other reasons to be specified:
- You should check the expiring date of the test or look for visible damages.
- Make sure that the threshold of the test is 20 International Units of the pregnancy hormone (hCG) per millilitre in blood. If it is not the case, and the test is sensitive to higher thresholds, you might get a false negative. Provided that this happens to you, wait at least one more week so the levels of hCG are higher and can be detected by the pregnancy test.
- Loss of the embryo. If there was pregnancy, it came to an early end and there has not been bleeding yet, the pregnancy test will result negative.
Other reason for the test to be negative is that the test is not taken at the appropriate time being, thus, recommended to be taken again about five days after to confirm the results. Nevertheless, when the results of the pregnancy test are positive, there is no doubt whatsoever. Even though there are false negative test results, there are no false positive results, and if the positive result turns out to be false, it might be because of a tumor or a reaction to the test.
As we have already mentioned, a woman can feel all the pregnancy symptoms and, still get negative results in the pregnancy test. However, if the symptoms persist, the woman should go to the doctor as s/he will be able to give her the right answer.