Menstruation that is bright red in color, like water, is clinically common in the following diseases: 1, due to submucosal uterine fibroids, due to submucosal fibroids is to grow into the uterine cavity, so that the uterine cavity is relatively large, and affect the uterine contraction, blood sinus opening, which will lead to the menstrual blood is bright red in color. 2, due to certain diseases of internal medicine, such as coagulation disorders or thrombocytopenia and lead to menstrual blood bright red. 3, if this situation has a history of menopause, it may be the symptoms of pre-menstrual abortion or inevitable abortion, must be ruled out pregnancy. Reduced and lead to menstrual blood is bright red. 3, if this situation ever appeared in the history of menopause, it may be a symptom of preterm miscarriage or inevitable miscarriage, and must be ruled out the possibility of pregnancy. In addition, this situation should be taken seriously, it is recommended to do routine blood tests, coagulation time tests, ultrasound and blood HCG laboratory tests.