1. Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong 510515, P.R. China
2. Key Laboratory for Major Obstetric Diseases of Guangdong Province, Key Laboratory for Reproduction and Genetics of Guangdong Higher-Education Institutes, Guangzhou Institute of Obstetrics and Gynecology, The Third Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong 510150, P.R.�China