This question is rather disputable among women. If you count from the date of sex act, then take this test in 2 weeks. So the right question is 14 days after sex.

Why Should a Woman Wait for So Long for a Period?

The matter is that after sex spermatozoa try to get to female egg cell. It takes about 1-2 days.

Then conception happens. But a fertilized egg cell should get to the womb. This process may take 6-7 days more. After getting to the womb, the egg cell takes root to its wall. After this a chorial gonadotropin hormone starts producing – the one, pregnancy tests react to.

Chorial gonadotropin is produced under pregnancy, acute diseases and in case of some specific drugs intake only (which contain this hormone in a synthesized form).to take a pregnancy test

Each express test has its sensitivity. The less number of hCG hormone it indicates, the higher sensitivity is. To define how to use a pregnancy test, read the instruction about its sensitivity in figures and have a look at growth table of hCG under pregnancy.

Of course one can start taking this test in 10 days before menstruation delay. Probably, hCG is already producing and can be fixed by means of express – diagnostics.  Keep in mind, that one should taking into account some nuances. For example the second strip can be too light. However, it should be considered as a positive result if you followed the instruction while taking this test. Also the second strip can be shown in several hours; however such test is considered to be a false one. False-positive result is possible in case you dip the strip deeper than it’s indicated on strip. Anyway, it’s recommended to take a test for hCG and repeat the test once again in a week. After the delay of menstruation, it’s possible to take a pregnancy test in two days. Or you can take it within the first day of the delay. By this time one can notice some other symptoms, such as toxicosis, elevated temperature and swollen mammary glands. If a woman is pregnant for the second time, she doesn’t need any tests at all!determination of pregnancy

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