1. Department of Obstetrics and Gynecology, Shanghai General Hospital Affiliated with Shanghai Jiao Tong University School of Medicine, Shanghai 200080, P.R. China
2. Department of Obstetrics and Gynecology, International Peace Maternity and Child Health Hospital Affiliated with Shanghai Jiao Tong University School of Medicine, Shanghai 200030, P.R. China
3. Department of Obstetrics and Gynecology, Shanghai Ninth People's Hospital Affiliated with Shanghai Jiao Tong University School of Medicine, Shanghai 200011, P.R. China