What is the reason for less menstrual flow after Qing Dynasty?

After curettage will cause endometrial damage, but also easy to cause infection. After curettage less menstruation, more common causes are cervical adhesions or intrauterine adhesions, resulting in menstrual blood can not be smoothly discharged, will show a decrease in menstrual volume or menstrual blood clots, showing dysmenorrhea and other abnormal phenomena; there may be too many times of uterine curettage, uterine curettage surgery, endometrial damage, endometrial thinning, resulting in reduced menstrual volume. In addition, if the patient has an endocrine disorder, such as reduced estrogen secretion, the endometrium will be relatively thin and menstrual volume will decrease. Some diseases such as premature ovarian failure, hyperthyroidism or PCOS will also cause menstrual volume to decrease.