The failure to detect the test paper after pregnancy is common in the following situations: First, the time of pregnancy is relatively short and the HCG concentration in urine is relatively low, so the positive result cannot be detected with the early pregnancy test paper at this time, and it is better to give the test after thirty-five days of menopause, and most of them will show positive results. Second, too much water was drunk before the urine was taken, resulting in dilution of the urine, so a false negative result is detected. Third, the test paper has expired or bought back the test paper is not well stored, there is a chemical contamination, this time also can not detect pregnancy. So when testing, be sure to know if the test strips have expired, and do not drink too much water before taking the urine specimen.