The following cases can not detect whether pregnancy: first, when ectopic pregnancy, because the blood HCG is relatively low compared to the blood HCG of intrauterine early pregnancy, so when using early pregnancy test paper to detect, it may not detect whether pregnancy; second, because of the relatively short time, because the pregnancy test stick can only be detected in the fertilization of the egg in the bed of the seventh day or so, so just stopped menstruation, some people are in a hurry to check, but also may not be able to detect the pregnancy; third, urine dilution, due to drinking too much water during the pregnancy test, the urine is diluted and watered down, it also can’t detect pregnancy. So don’t drink too much water starting the day before the pregnancy test to avoid dilution of urine; fourth, pregnancy test sticks that are expired or improperly stored and damp will also fail to detect pregnancy.