Failure to detect pregnancy with test strips may be caused by expired test strips, shorter gestation period or drinking a lot of water before the test. 1. Expired test strips: Test strips that have expired, or test reagents in the test strips that have failed due to improper storage, etc., may lead to deviations in the test results, resulting in the situation of not being able to detect a pregnancy when you are already pregnant. It is recommended to store the bought pregnancy test paper properly and confirm the shelf life of the test paper before use. 2. Short pregnancy: If the pregnancy is very short, the HCG (human chorionic gonadotropin) in the pregnant woman’s body has not reached a high level, which may lead to the situation that the test strips can not detect the pregnancy. In this case, it is recommended to wait for a period of time before taking the test again. 3. Drinking a lot of water before the test: If a pregnant woman drinks too much water before the test, it may cause the urine to be diluted and give a false negative result. It is recommended that you do not drink water before the test, or drink a small amount of water. If you can’t detect the test paper when you are pregnant, it is recommended that you consult a doctor in time to improve the blood HCG test and ultrasound examination to clarify the specific situation of the pregnant woman.