1. Center for Reproductive Medicine, Renji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200135, P. R. China.
2. Shanghai Key Laboratory for Assisted Reproduction and Reproductive Genetics, Shanghai 200135, P. R. China.
3. Department of Obstetrics and Gynecology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
4. Department of Obstetrics and Gynecology, No. 401 Hospital, Qingdao 266100, P. R. China.