1. Department of Obstetrics & Gynecology, The Second Affiliated Hospital of Sun Yat-Sen University, Guangzhou, Guangdong, China
2. Department of Obstetrics & Gynecology, General hospital of Guangzhou Military Area, Guangzhou, Guangdong, China
3. Department of Obstetrics & Gynecology, The Second Affiliated Hospital of Sun Yat-Sen University, Guangzhou, Guangdong, China,