1. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Xiamen University, Xiamen, Fujian 361003, P.R. China
2. Central Laboratory, The First Affiliated Hospital of Xiamen University, Xiamen, Fujian 361003, P.R. China
3. Department of Obstetrics and Gynecology, Zhujiang Hospital of Southern Medical University, Guangzhou, Guangdong 510280, P.R. China