1. Department of Gynaecology and Obstetrics, Zhuji Affiliated Hospital of Shaoxing University, Zhuji, Zhejiang 311800, P.R. China
2. Department of Gynecology, Shaoxing People's Hospital and Shaoxing Hospital, Zhejiang University School of Medicine, Shaoxing, Zhejiang 312000, P.R. China
3. Obstetrics Department, Jinhua Maternal and Child Health Hospital, Jinhua, Zhejiang 321000, P.R. China