We see a lot of patients who come to the clinic with low menstrual flow, but how do we define low menstrual flow? Is low menstrual flow a disease? First of all, we need to understand that a normal menstrual cycle should have a volume of 20-60 ml, less than 20 ml is considered as a low menstrual flow. (Usually the standard is whether the surface of a daily sanitary napkin is wet or not, if the surface of a daily sanitary napkin is wet, it is generally considered that the menstrual volume is more than 5ml, and if it is wet, it is considered that the menstrual volume is more than 15ml). Generally speaking, a sudden low menstrual flow is caused by pathological factors. So what are the causes of scanty menstruation? It can be caused by declining ovarian function, damaged endometrium, adhesions, infection with tuberculosis, endocrine factors and drugs: 1. Declining ovarian function: When the ovarian function declines, estrogen level decreases, which affects the proliferation of endometrium and reduces menstrual flow. Ovarian function can be assessed by measuring basal sex hormones such as FSH, LH, E2 and ultrasound to make a clear diagnosis. 2, endometrial damage: history of uterine operation (such as abortion, hysteroscopic operation, or even cesarean section) may result in endometrial basal layer damage and endometrial thinning during improper operation, excessive force or repeated operation, and reduced menstrual flow or even amenorrhea. 3. Adhesions: The adhesions of the uterine cavity and cervical adhesions caused by the abortion procedure will block the menstrual discharge channel and make the menstrual blood flow out poorly, manifesting as low menstrual flow and accompanied by dysmenorrhea due to the accumulation of seminal blood in the uterine cavity. The history shows that there is a history of uterine operations such as abortion. 4. Infection with tuberculosis: Infection of the endometrium with tuberculosis can cause damage to the endometrium or produce adhesions in the uterine cavity, resulting in reduced menstrual flow and even amenorrhea. Usually these patients have difficulty conceiving due to severe endometrial damage, despite successful anti-tuberculosis treatment. 5. Endocrine diseases: such as hyperprolactinemia, polycystic ovary syndrome, hypothyroidism and other endocrine abnormalities can lead to reduced menstrual flow or even amenorrhea. The diagnosis can be confirmed by measuring hormones such as PRL, FSH, LH, FSH, T3, T4, etc. 6, drugs: such as the recent use of contraceptives or antipsychotic drugs (such as chlorpromazine, methiodiazine, fenadine, etc.) can reduce the amount of menstruation. 7, mental and psychological factors: some little girls due to excessive dieting or pressure to go to school and other physical and mental factors, resulting in transient menstruation or amenorrhea. For different causes, the low menstrual volume should be treated for the right reasons. Therefore, low menstrual flow is a pathological manifestation and early medical consultation is advocated.