Establishment of regular menstrual cycles is a key component of reproductive maturation and a recognized vital sign for health and well-being. Irregular menstrual cycles are especially common for the first 2-3 years after an adolescent's first menstrual period (i.e., menarche), which delays the identification and diagnosis of early reproductive disturbances such as polycystic ovary syndrome (PCOS). The purpose of this research study is to determine whether the ovary can serve as a reliable predictor of normal or abnormal development by following the trajectory of ovarian morphology in conjunction with menstrual cyclicity using 3D transabdominal ultrasound imaging in a prospective cohort study of adolescents. A secondary objective is to identify potential environmental factors such as diet and the gut microbiome which influence the trajectory towards normal or abnormal reproductive development.