The usual onset of menarche is between the ages of 9 to 17.7 years with the median age 12.8 years (Griswold, 2004). Cycles vary in frequency from 21 to 40 days, and occur regularly. Bleeding lasts 3 to 8 days and the usual blood loss averages 30 to 80 mL. The classic cycle of 28 days occurs in only 15% of menstrual cycles.