1. Department of Gynecology and Obstetrics, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
2. Department of Gynecology and Obstetrics, The Affiliated Hospital of Medical College of Ningbo University, Ningbo, Zhejiang 315020, P.R. China
3. Department of Obstetrics and Gynecology, Obstetrics and Gynecology Hospital, Fudan University, Shanghai 200012, P.R. China