1. Department of Obstetrics and Gynecology, Peking Union Medical College Hospital; Peking Union Medical College & Chinese Academy of Medical Science; Shuaifuyuan No. 1 Dongcheng District Beijing 100730 P.R. China
2. Department of Pathology, Peking Union Medical College Hospital; Peking Union Medical College & Chinese Academy of Medical Science; Beijing 100730 P.R. China