1. Department of Obstetrics, The Second Clinical Medical College, Jinan University, Shenzhen People's Hospital, Shenzhen 518020, Guangdong, China
2. The First Affiliated Hospital, Jinan University, Guangzhou 510000, Guangdong, China
3. Department of Obstetrics and Gynecology, The Second Xiangya Hospital, Central South University, Changsha 410000, Hunan, P.R. China
4. The First Affiliated Hospital, Department of Obstetrics and Gynaecology, Hengyang Medical School, University of South China, Hengyang 421001, Hunan, China
5. Xiangya Stomatological Hospital, Central South University, Changsha 410008, Hunan, China