The absence of menstrual bleeding may be caused by partial shedding of the endometrium, usually a small amount of brown blood, which is a normal phenomenon. In addition, it may also be caused by disease factors, such as luteal insufficiency, ectopic pregnancy, vaginitis, cervical and uterine lesions, etc.: 1. Luteal insufficiency: The corpus luteum secretes progesterone after ovulation, which thickens the endometrium to a certain thickness before the endometrium sheds and menstruation occurs. When luteal insufficiency often causes irregular menstruation, delayed menstruation, frequent menstruation and other physiological phenomena, can also cause menstruation did not come out a little blood; 2, cervical lesions: such as severe erosion of the cervix, cervical polyps, submucosal fibroids out of the cervical opening, cervical precancerous lesions, cervical cancer and other diseases, can appear a small amount of vaginal bleeding; 3, uterine lesions: such as endometrial polyps, submucosal fibroids, endometriosis The symptoms are mild and can cause a small amount of bleeding during non-menstrual period; 4. It is easy to cause pre-eclampsia abortion. If the menstruation is delayed for more than 7 days with vaginal bleeding, it may be caused by pre-eclampsia abortion after pregnancy, which will lead to a small amount of vaginal bleeding; 6. Ectopic pregnancy: it is caused by the fertilized egg being laid and developed outside the body cavity of the uterus, which mainly manifests as menopause, abdominal pain and vaginal bleeding. After the death of the embryo there is often irregular vaginal bleeding with a small amount of red color, which usually does not exceed the amount of menstruation.