1. Department of Obstetrics and Gynecology, Jinzhou Medical University, Jinzhou, Liaoning 121000, P.R. China
2. Reproductive Center, Qingdao Women and Children's Hospital, Qingdao, Shandong 266000, P.R. China
3. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Jinzhou Medical University, Jinzhou, Liaoning 121000, P.R. China