Regular menstruation but suddenly become less consider excessive dieting, emotional abnormalities and other physiological factors, may also be due to uterine adhesions, polycystic ovary syndrome and other pathological factors. 1. Physiological factors: if the female patients usually eat and rest irregularly, excessive dieting or mental stress, depression and tension and other negative emotions, there will be a sudden change in the amount of menstruation, need to adjust personal habits. 2. Uterine cavity adhesion: the pathogenesis of this is not clear, and is mostly considered to be related to endometrial trauma, low estrogen levels, infections, genetics and other factors. Patients often appear menstruation decrease, or even amenorrhea, can also be manifested as regular menstruation but suddenly become less. Some patients may also have symptoms such as cyclic abdominal pain. 3. Polycystic Ovary Syndrome: The cause of this disease is still unclear, and it is mostly related to environmental and genetic factors. Usually, patients will have scanty menstruation, low menstrual flow or amenorrhea, etc. Some patients may also have regular menstruation but suddenly have low menstrual flow. Some patients may also suffer from acne, hirsutism, infertility and cardiovascular diseases in middle-aged and elderly patients. It is recommended that patients who experience regular menstruation but suddenly have less menstrual flow should first rule out physiological factors, and if the condition is considered to be caused by a disease, it is recommended that they consult a doctor in a timely manner and follow the doctor’s instructions for specific treatment.