The sudden shortening of the menstrual cycle is considered to be related to insufficient secretion of follicle stimulating hormone or low estrogen level, which causes the follicular phase to become shorter, resulting in a shorter menstrual cycle. Normally, the menstrual cycle is divided into follicular phase, luteal phase and menstrual phase, the normal menstrual phase is usually around 3-5 days, with the longest not exceeding 7 days, and the luteal phase is relatively stable usually around 14 days, so the most likely cause of menstrual cycle changes is Changes in the follicular phase. Under normal circumstances, it is normal for the menstrual cycle to be 21-35 days, which means that it is normal for the menstruation to be early or delayed by a week. If the shortening of the menstrual cycle is less than 21 days, it is advisable to go to the hospital to test the female hormone six, if the follicle stimulating hormone and estrogen value is low, you can treat it by hormone supplementation.