The most common reason for the sudden prolongation of menstruation is incomplete atrophy of the corpus luteum. If the corpus luteum does not atrophy in time, the estrogen and progesterone in the body will retreat more slowly, and the shedding of the endometrium is not very complete, so the menstruation time will be prolonged. If it is more than seven days, it is not normal. There is another reason, there may be submucosal fibroids, endometrial polyps, polyps of the cervix, all of which may cause prolonged menstruation. So when this phenomenon occurs, you need to go to the hospital as soon as possible to do a checkup, first of all, do ultrasound examination, if ultrasound examination is not a problem, it is caused by endocrine disorders, which need to be treated.