GnRH stimulates secretion of LH and FSH which causes the ovary to produce estrogens. Subsequently changes of pubey occur including breast development (thelarche), development of pubic and axillary hair (pubarche), the growth spu (peak height velocity), and onset of menstruation (menarche). Thelarche (breast development) is the first sign of pubey (Tanner stage B2). It usually begins between 8 and 10 years of age and is associated with increased estrogen production. Pubarche (development of pubic and axillary hair) is the second stage in maturation and typically occurs between 11 and 12 years of age. Axillary hair usually appears after the growth of pubic hair is complete. Menarche (onset of menstruation) usually occurs 2-3 years after thelarche at an average age of 11-13 years. Initial cycles are often anovulatory and irregular. Ref: Blueprints Obstetrics & Gynecology By Tamara L. Callahan, Aaron B Caughey, Aaron B Caughey, M.D., 2008, Page 212 ; Obstetrics and Gynaecology at a Glance By Errol R. Norwitz, John O. Schorge, 2010, Page 49 ; Nelson Textbook of Paediatrics 17th edition page 1882