The pregnancy test paper detects the level of human chorionic gonadotropin HCG in the body, and the increase in HCG level is not seen as a cause of pregnancy, but in the absence of pregnancy but the body has certain pathological factors or incorrect operation and other reasons, there may be a deep and a light situation. Pregnancy test paper is through the detection of HCG levels in the body to determine whether the pregnancy, HCG is mainly produced by trophoblast cells, under normal circumstances in the 14 days after fertilization due to the increase of HCG in the urine, the test paper may appear a dark and light two red lines. However, if you are not pregnant but have some pathological factors, such as trophoblastic diseases (hyperemesis gravidarum, choriocarcinoma, etc.), due to the proliferation of trophoblast cells, the level of HCG in the body will also increase, so the test paper may also show one dark and one light or even a strong positive performance. In addition, due to the formation of trophoblast cells in ectopic pregnancy, HCG will also be produced in the body, but HCG is often lower than that of normal pregnancy, so the test paper may show one dark and one light. Patients with germ cell tumors, lung cancer, adrenal tumors, etc. can produce HCG in their bodies, and the test paper can also show one dark and one light. In addition, due to improper operation or the test paper has expired and other factors, the test can also be inaccurate in the case of non-pregnancy. Therefore, the appearance of a dark and light test paper can not be sure of pregnancy, but also need to be based on blood HCG, ultrasound, menopause history and other comprehensive analysis of the reasons.