If you have intercourse during ovulation without contraceptive measures, you have a high chance of pregnancy, which will cause delayed menstruation. If the pregnancy time is too short to be detected by using early pregnancy test paper, you can usually go to the hospital to have a blood test for HCG about 10 days after intercourse to determine the pregnancy, and the blood test is more accurate. If you use early pregnancy test paper, there will be some errors because it is affected by the concentration of urine and the amount of hormones in your body. Incorrect use of the test strips will also affect the test results. It is best to use morning urine when using early pregnancy test strips, and it is recommended to use them according to the instructions, only when they are used correctly will the test results be more accurate.