Menstruation once every 18 days is generally considered abnormal. The interval between the first day of two menstrual periods is usually referred to as the menstrual cycle, which tends to last from 21 to 35 days, with an average of 28 days, and the duration of each period is usually from 2 to 8 days, with an average of 4 to 6 days. A menstrual cycle of 18 days is considered to be out of the normal range and is considered to be an abnormal menstrual cycle. This condition is mostly considered to be related to endometrial polyps, uterine fibroids and other diseases, patients need to pay attention to it in time, and after a systematic examination to clarify the cause of the disease, take reasonable treatment measures under the guidance of the doctor, so as to avoid aggravation of the condition. It is recommended that patients actively seek medical treatment according to their own situation and cooperate with doctors for relevant treatment.