Menstruation refers to the days when the menstrual blood flows from the vagina. A cycle is the time from the first day of menstruation to the last day before the next menstruation. This is different for every woman but normally takes happens about every 21 to 35 days. Usually, menstrual bleeding occurs 28 days after the last period. Normally menstruation starts with heavier bleeding, which becomes lighter over the next few days. The light red blood becomes darker and darker. The menstrual period lasts three to six days and at the end, there may well be spotting with old, brownish blood. As a rule, women lose a total of about 50-60 millilitres of blood during menstruation.

Cycle disturbances or irregularities in the female cycle can occur, which relate to the frequency, duration and strength/heaviness of menstruation. They are normal immediately after the first menstrual period, as menstruation and hormonal changes must first settle down.

There are many causes of cycle disturbances. Since the cycle is hormonally controlled, hormonal disorders, as well as diseases of the female sexual organs, are most often the cause of changes. Moreover, medication, genetic disposition, physical or psychological stress can also be the cause of cycle problems.