If a woman’s ovaries are functioning normally and her uterine lining is not damaged, it is not possible for her to menstruate with an endometrium of 5 millimeters. Normally, a woman’s endometrium can reach about 5 mm within 3-5 days after menstruation, and by the time of ovulation, the endometrium should be at least 0.7 cm or more, and at least 1.0 cm or more before menstruation. If the patient’s ovaries are not functioning normally, for example, if there is polycystic ovary syndrome or if the patient’s uterine lining is damaged with localized adhesions and other special conditions, the endometrial lining thickness of 5 millimetres can lead to menstruation, but the amount of menstruation will be very low. In this case, the patient can have fluctuations in hormone levels, which can affect the proliferation and exfoliation of the endometrium, so it can lead to bleeding. If the bleeding is cyclical and regular it is menstruation, if it is non-cyclical and irregular it is irregular vaginal bleeding and not normal menstruation.