In most cases, pregnancy can be detected with a test strip after 14 days of coitus. After coitus, sperm and egg combine to form a fertilized egg, which gradually develops into an embryo, and the trophoblast layer of the embryo secretes human chorionic gonadotropin, which normally begins to be secreted 10-14 days after coitus, and the secretion of human chorionic gonadotropin gradually increases. The level in blood and urine will obviously and gradually increase, the use of test strips is also to test the level of human chorionic gonadotropin in the urine, so generally 14 days after coitus, most of the test strips can be used to detect pregnancy. If the 14 days of cohabitation using test strips did not detect pregnancy, you can also go to the hospital to draw blood to perfect blood human chorionic gonadotropin, generally 7-10 days after cohabitation can be measured whether the pregnancy, the results of the blood is also more accurate. If the test paper does not detect pregnancy after 14 days of cohabitation, you can take another test after 2-3 days or go to the hospital offline for further blood tests.