Clinical Pitfall Related to the Measuring of Serum Estradiol Concentrations Under Gel Transdermal Estrogen Replacement Therapy: A Case Report of Iatrogenic Primary Ovarian InsufficiencyTakeki Sato1, Masahito Tachibana1,2, Hiroaki Hiraga1, Emi Yokoyama1, Zen Watanabe1, and Masatoshi Saito1,2Department of Obstetrics and Gynecology, Tohoku University Hospital, 1-1 Seiryo-machi, Aoba-ku, Sendai-shi, Miyagi 980-8574, JapanDepartment of Perinatology, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai-shi, Miyagi 980-8574, Japan