Progesterone Suppression of Nocturnal LH Increases in Pubertal Girls

The purpose of this study is to learn more about how gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) pulses are controlled during puberty. In this study, the investigators aim to discover whether or not giving 2 small doses of progesterone to early pubertal girls will prevent the nighttime increase of GnRH and LH pulses. From the information gathered in this study, the investigators may be able to learn more about how menstrual cycles are normally established in girls during puberty. Ultimately, if these normal processes can be understood, the investigators may be able to better understand abnormalities of puberty.