1. Peking Union Medical College Hospital, Beijing, China;
2. Zhongda Hospital, Southeast University, Nanjing, China;
3. Department of Obstetrics and Gynecology, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China;
4. Family Planning Research Institute of Tongji Medical College of Huazhong University of Science and Technology, Wuhan, China;
5. Southwest Hospital, Third Military Medical University, Obstetrics and Gynecology, Chongqing, China;
6. Peking University Third Hospital, Beijing, China;
7. Merck & Co., Inc., Kenilworth, NJ, USA