Expired pregnancy tests are not valid. The HCG antibodies of an expired pregnancy test are no longer valid and cannot bind to the antigens in the urine and show a reaction. If you test with an expired pregnancy test, the result is inaccurate and the measurement result may appear as a white plate, i.e. no color appears; there may also be a positive result, but it has no reference value. So when you buy them, you should pay attention to check the production date on the box and not to use early pregnancy test papers that have expired or are damp or hot. Since the correct test rate of pregnancy test strips varies greatly, ranging from 50% to 98%, in addition to the production date, special attention should be paid to the testing time and operation steps when using them: 1) testing time: it is recommended to use morning urine for testing, because it is generally believed that the concentration of morning urine is higher and the accuracy of testing morning urine will be higher; 2) operation steps: before conducting self-test, you should read the relevant instructions carefully and then follow them carefully. Then follow the instructions carefully; 3. Other: During the test, we should observe whether there are positive results caused by non-pregnancy factors, such as endometrial hyperplasia, blood in the urine, ovarian tumors, incomplete miscarriage, etc., which can cause positive reactions. Therefore, in order to confirm pregnancy, it is recommended to check blood β-HCG and combine it with medical history as well as ultrasound examination to clarify the diagnosis.