A negative urine pregnancy test before menstruation does not mean that the patient is not pregnant, and there is still a possibility that the patient is pregnant. This is mainly because of the following two reasons: First, the accuracy of the urine pregnancy test is not 100%, there is the possibility of false negatives, so the patient as long as there is no menstruation, you can continue to monitor the urine pregnancy test or check the blood chorionic gonadotropin to confirm. Secondly, if the patient’s examination is not at the right time, even if the blood chorionic gonadotropin is examined, there may be errors. This is because the patient’s determination of whether or not she is pregnant is not based on the timing of her menstrual period, but rather by the timing of the patient’s ovulation or the timing of coitus. If ovulation is confirmed, blood HCG after 7 days and urine HCG after 10 days can determine pregnancy more accurately. If ovulation is not confirmed, a blood test after 10 days and a urine test after 13 days can accurately determine pregnancy. If the test is conducted within a very short period of time after intercourse, it may not be detected, mainly because the concentration of HCG in the blood and urine will not increase until the fertilized egg has implanted in the bed, so the test cannot be detected.