There are many reasons why menstrual flow is low during menstruation, which may be related to abnormal ovarian function and endocrine dysfunction. 1. Abnormal ovarian function: If there is only one day of menstrual flow during menstruation, it may be related to abnormal ovarian function, and when ovarian function is insufficient, estrogen will be lowered accordingly, which will lead to the emergence of such symptoms. 2. Endocrine disorders: If a woman has recently stayed up late, is under stress or has an irregular diet, it may cause endocrine disorders, leading to low menstrual flow. In addition, endocrine disorders, such as polycystic ovary syndrome and pituitary tumors, can also lead to such a situation. There may be other reasons for the low menstrual flow, so it is recommended to go to the hospital in time for a complete examination to clarify the cause of the problem and then follow the doctor’s instructions to give targeted treatment or therapy.