1. Department of Obstetrics and Gynecology, The Second Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China
2. Department of Obstetrics and Gynecology, Shandong Second Provincial General Hospital, Jinan, Shandong, China
3. Department of Obstetrics and Gynecology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.