1 Centre for Reproductive Medicine, Department of Obstetrics and Gynaecology, Peking University Third Hospital, Beijing 100191, China; National Clinical Research Centre for Obstetrics and Gynaecology, Beijing, China; Key Laboratory of Assisted Reproduction, Peking University, Ministry of Education, Beijing, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, Beijing, China.
2 Centre for Reproductive Medicine, Department of Obstetrics and Gynaecology, Peking University Third Hospital, Beijing 100191, China; National Clinical Research Centre for Obstetrics and Gynaecology, Beijing, China; Key Laboratory of Assisted Reproduction, Peking University, Ministry of Education, Beijing, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, Beijing, China. Electronic address: jie.qiao@263.net.