Menstrual period is menstruation. Menstruation with more or less than one month may be caused by endocrine disorders, low ovarian function and other reasons, but sometimes it is also a normal phenomenon. 1. Endocrine disorders: some women have mental stress, environmental changes, excessive dieting, etc., which may affect the body’s endocrine system, leading to endocrine disorders, which may also affect menstruation, manifesting as one month of heavy menstruation and one month of light menstruation. 2. Low ovarian function: When some women have low ovarian function, it may lead to abnormal hormone levels in the body, which sometimes manifests as one month of heavy menstruation and one month of light menstruation. 3. Normal phenomenon: During puberty, due to the imperfect development of the gonadal axis, or during menopause, due to the unstable secretion of hormones in the body, it is possible to have more than one month of menstruation, and less than one month of menstruation. This is usually normal. It is recommended to go to the hospital for ultrasonography and sex hormone test to determine the cause of menstruation, and then follow the doctor’s instructions to treat the cause of menstruation.