Women donate blood from a vein, which has nothing to do with menstruation. Menstruation is the process of blood flowing out of the vagina due to the withdrawal of estrogen and progesterone, resulting in the flow of endometrial fragments mixed with blood. The amount of menstruation is mainly related to the thickness of the lining and the blood supply to the uterus. Low menstrual flow is usually seen in patients with endocrine disorders of the ovaries or polycystic, or due to adhesions in the uterine cavity. In other cases, repeated abortions may cause damage to the endometrial tissue, resulting in low menstrual flow. Therefore, if you have reduced menstrual flow, you should go to the gynecology department to have an ultrasound and hormone test to see the cause of the reduced menstrual flow, and then treat the symptoms according to the results.