The nomenclature relating to AUB has been thoroughly discussed in Chapter 3. To reiterate, clinicians and investigators use a variety of terms to describe disorders of menstrual bleeding, often commingling a variety of descriptive and diagnostic terms and phrases. The fact that similar terms are used in different ways in different countries and even by different gynecologists within a single practice setting has confounded both the design and interpretation of clinical investigation in this arena. 1 As a result, the simplified nomenclature discussed previously will be used to facilitate discussion about the definitions and symptoms of AUB. These definitions generally use the 5th and 95th centiles to discriminate between normal and abnormal menstrual function.