In women, testosterone is generally converted to estrogenic compound of 18–carbon steroid with aromatic A–ring (estradiol, estriol, and estrone) through actions of enzyme aromatase (Figure 3–9) (Purohit and Reed 2002). The strongest active form of estrogen is estradiol, which is subdivided into two isoforms, 17α–estradiol and 17β–estradiol (Fang et al. 2001).