Androgen oxidation aromatization

The primary estrogen in premenopausal women is 17-P-estradiol (E2), which is synthesized by developing ovarian follicles. Estradiol is oxidized to estrone (El) and then to estriol (E3). Estrone is also produced in peripheral tissues by aromatization of androstenedione, an androgen precursor that is produced by both the ovaries and the adrenal glands after the menopause, estrone produced in this way becomes the predominant estrogen. All of the estrogens are sulfated and glucuronidated before excretion. 

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