1. Department of Obstetrics and Gynecology, Liaocheng People's Hospital, Liaocheng, Shandong 252000, P.R. China
2. Department of Pathology, Liaocheng People's Hospital, Liaocheng, Shandong 252000, P.R. China
3. Department of Obstetrics and Gynecology, Liaocheng Third People's Hospital, Liaocheng, Shandong 252000, P.R. China