1. Principle of pregnancy test paper pregnancy test paper pregnancy test is to determine whether you are pregnant by detecting human chorionic villi (hCG) in urine. hCG is a hormone secreted by the chorion of the early embryo and begins to be secreted after the fertilized egg implants. The antibodies on the test strip can recognize and bind to hCG, producing a positive reaction. 2. Accuracy of test strips to detect pregnancy The accuracy of test strips to detect pregnancy depends on the time and method of use. It is usually recommended that after the expected start of the menstrual cycle