What is the definition of primary amenorrhea?

Primary amenorrhea is defined as the absence of menstruation by a certain age, specifically up to 15 years old, which is aligned with the normal onset of menstruation for most individuals. This definition is grounded in the understanding of developmental milestones in female adolescents. By the age of 15, most individuals who are biologically female should have begun their menstrual cycles; thus, failure to menstruate by this age is a clinical indicator warranting further evaluation for potential underlying conditions or health issues.

In contrast, the other options relate to different menstrual irregularities. For example, no menses for 6 months corresponds to secondary amenorrhea, not primary, which is characterized by the cessation of menstruation after it has already begun. Additionally, menses lasting longer than 7 days or presenting as irregular and heavy bleeding both refer to abnormal menstrual patterns, rather than the absence of menstruation altogether that is characteristic of primary amenorrhea.