1. Department of Obstetrics and Gynaecology, Qilu Hospital of Shandong University, Jinan, Shandong 250012, P.R. China
2. Department of Obstetrics and Gynaecology, The Second Affiliated Hospital of Shandong First Medical University, Tai'an, Shandong 271000, P.R. China
3. Department of Pathology, Feicheng Hospital Affiliated to Shandong First Medical University, Tai'an, Shandong 271600, P.R. China