Amenorrhea is the absence of menstruation.

There are two types of amenorrhea, primary and secondary. Primary amenorrhea is delayed menarche (the first menstrual period) and is defined as any one of three conditions:

1.) absence of menarche by age 16 with otherwise normal pubertal development (development of breasts and/or pubic hair)

2.) absence of menarche by age 14 with delayed pubertal development

3.) absence of menarche two years after puberty is otherwise completed

Family history should be taken into consideration in any adolescent with primary amenorrhea. Mothers who started to menstruate late will often have daughters who also menstruate late.

Secondary amenorrhea is the absence of menstruation after menarche has taken place. Although it is not uncommon for menstrual periods to be irregular during early adolescence, periods usually become regular with in 18 months after the first one. After that time, it is considered abnormal for an adolescent to miss three consecutive periods...