All modern methods of diagnosing pregnancy in the early stages of the test are based on the same principle of action: they react to the hCG hormone, which begins to be produced by the woman's body on the seventh day after fertilization.
The difference between the models lies in their sensitivity. Products of a new generation, have not only a high price, but also increased accuracy. The reliability in this case is 98-99%. It is important to know on which day of a delay in menstruation to take a test. Gynecologists recommend performing the procedure several times: immediately after the delay, after 5-7 days and after 10-12 days.