Aunt usually refers to a woman’s menstrual period, the third day of menstrual blood black and small amount may be due to the endometrial lining of the uterus thin, endometrial polyps and other reasons related. 1. Thin lining of the uterus: when a woman’s menstrual period is dark and the amount of blood is small, it may be due to the thin lining of the uterus, which will lead to slower blood circulation in the pelvis, and the endometrium will peel off, and then there will be a problem of untimely discharging. 2. Endometrial polyps: The dark color and low amount of blood during menstruation may also be caused by the presence of endometrial polyps. Endometrial polyp ischemia, necrosis, submucosal leiomyoma necrosis leads to a longer time in the uterine cavity deposition, and then appear this symptom. The third day of menstruation, black color and low volume may also have other reasons, it is recommended to go to the hospital, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.