Decreased menstrual flow at the age of 40 is often caused by the following reasons: first, endocrine disorders, where the decrease in estrogen causes decreased menstrual flow. The second, the development of ovarian decline, can also cause a decrease in menstrual flow. The third, polycystic ovary syndrome. The fourth, endometrial tuberculosis. The fifth one, a relatively weak constitution and anemia, can also lead to decreased menstrual flow. In addition, if there has been a recent uterine operation, resulting in uterine adhesions, it can also cause a decrease in menstrual flow. Therefore, in this case, first of all, it is recommended to have a blood test for sex hormone six on the second or third day of menstruation and then give the appropriate treatment according to the results, mainly to find out whether the ovaries are still functioning normally. In addition, ultrasound examination is also recommended, together with the clinical history for comprehensive analysis.