1. Institute for Fetology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China
2. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China
3. Department of Gynecology and Obstetrics, Dushu Lake Hospital Affiliated to Soochow University, Suzhou, Jiangsu 215100, P.R. China