So, we know that after fertilization, the level of the hCG hormone in the woman’s blood begins to rise, which indicates the presence of pregnancy. Having determined this substance, the test shows us a positive result - two strips. In fact, the test reacts to the presence of the hormone gonadotropin in the urine: when the level of hCG rises, a reagent appears on the second test strip.
HCG in the body of a pregnant woman is produced immediately after the implantation of the embryo into the uterine wall, first in the blood, and a little later in the woman's urine, and usually in the urine it is in a lower concentration than in the blood. Implantation, in turn, occurs 7-10 days after ovulation.
But at the same time, it must be borne in mind that the level of the hormone grows gradually, increasing daily, until it reaches a certain level, which the test is able to fix. This is the moment that sets the time frame.
That is, the test is able to "detect" the presence of the hormone gonadotropin in the urine of a pregnant woman no earlier than 11-15 days after the day of the last ovulation. The lower the sensitivity threshold of the test, the earlier it will be able to determine pregnancy and the more expensive it is.
Tests with a sensitivity of 10mIU / ml (as a rule, inkjet tests belong to this category) are able to determine a pregnancy that has taken place several (up to five) days before the expected period.
Tests with a sensitivity of 25 mIU / ml (in the form of strip strips) determine pregnancy from the first day of delay. But these are statistics. And there are individual cases with early or late implantation. Therefore, a premature test can often be wrong.
The probability of a test error is especially high if a woman has an irregular menstrual cycle. An early test in this case may show false negative results, because the gestational age may be very short for the reactive strip to work. A pregnancy test error is more likely the earlier the test was taken.
A pregnancy test with an irregular cycle does not make sense to carry out before a delay. The earliest time when this can be done is two weeks after ovulation, and the longest cycle should be taken as a guideline.
If you do not monitor this process, then it is recommended to test after a delay, and for greater reliability, it is best to repeat the test again, after a week or two. Regardless of the regularity of the cycle and other features of the female body, the reliability of the test will be the higher, the more clearly the rules for its implementation are observed. Any violation of the instructions may cause false results.
It is believed that in the morning a pregnancy test shows the most reliable results, since the concentration of hCG in morning urine is the highest. But if the delay is already large, then by and large it is possible to conduct a test at any time of the day.
A prerequisite is the observance of the rules of sterility: no foreign substances should enter the test liquid, and therefore the hands must first be thoroughly washed and wiped dry. Also, prepare a sterile collection vessel in advance.
The test strip must be immersed in the container with urine only to the level indicated on its canvas, and always on the side where it is indicated (where the reactive substance is contained).
You should not evaluate the test result earlier than the time indicated in the instructions (usually 5 minutes) or much later. After a long period of time, the results of any test are considered invalid.