1. Center for Reproductive Medicine, Ren Ji 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. Shanghai First Maternity and Infant Hospital, Tongji University School of Medicine, Shanghai 201204, P. R. China.
4. Department of Obstetrics and Gynecology, Oregon Health and Science University, Portland, OR 97239, USA.