1. Department of Obstetrics and Gynecology, The Second Affiliated Hospital of Harbin Medical University, Harbin 150086, Heilongjiang, P.R. China
2. Department of Obstetrics and Gynecology, First Affiliated Hospital of Wannan Medical College, Wuhu 241000, Anhui, P.R. China
3. Department of Gynecology, International Peace Maternity and Child Health Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 310000, P.R. China
4. Department of Obstetrics and Gynecology, Shenzhen Second People’s Hospital, First Hospital of Shenzhen University, Shenzhen 518000, Guangzhou, P.R. China