N91: Absent, scanty and rare menstruation

N91.0: Primary amenorrhoea

The uterus consists mainly of a layer of muscle and a lining of mucous membrane (mucosal lining). The mucosal lining receives a good supply of blood and steadily increases in size. Unless an egg is fertilized, a large part of the mucosal lining is shed and replaced. The menstrual bleeding starts when the mucosal lining is shed. The uterus is connected to the vagina. During your menstrual bleeding the mucosal lining is discharged through the vagina to the outside of the body along with some blood.

You have not yet had a menstrual bleeding. That can have various causes. Menstrual bleedings may not occur, for example, if the genital organs are not properly developed or are missing. Another reason they may not occur is a change in the levels of messenger substances in the body. Menstrual bleedings are controlled by various messenger substances.