There are many reasons for menstruation once in 3 months, which may include endocrine diseases, polycystic ovary syndrome, etc. If vaginal bleeding is not real menstruation, it may be abnormal vaginal bleeding caused by pregnancy factors, it is recommended to seek medical advice to clarify the cause. 1, endocrine diseases: bad living habits and bad emotions can lead to endocrine disorders, menstrual disorders or even amenorrhea, which require adjustment of lifestyle and status; abnormal function of endocrine organs, such as hypothyroidism, prolactinoma, etc. can lead to scanty menstruation, menstrual It is necessary to treat the original disease in time and adjust menstruation by supplementing estrogen and progesterone. 2. polycystic ovary syndrome: the cause is unknown and is generally believed to be caused by genetic and environmental factors, mainly manifesting as scanty menstruation, amenorrhea, infertility, hirsutism and acne, etc. Treatment can be progestin therapy, which can increase the level of hormones in the body or promote ovulation to relieve symptoms. 3. pregnancy factor: women will stop menstruating after pregnancy. However, if a pre-eclampsia miscarriage occurs and the patient does not detect her pregnancy, she mistakenly believes that her period is delayed for 3 months before it occurs. Pre-eclampsia can be treated with birth control, and pregnancy can be terminated when birth control is ineffective; 4, other: pelvic inflammatory disease, cervicitis, vaginitis and many other gynecological diseases, as well as malnutrition, liver disease, blood disorders and many other factors can lead to prolonged menstruation, and it is recommended to seek medical attention in a timely manner to clarify the cause and then treat it.