1. Department of Gynecology, Affiliated Hospital of Jining Medical University, Jining 272100, China
2. Depatment of Obstetrics, Pingdu People’s Hospital, Qingdao 266700, China
3. Department of Obstetrics, Wulian Country People’s Hospital, Rizhao 262300, China
4. Department of Obstetrics, Chifeng City Center Hospital Ningcheng Country, Chifeng 024200, China
5. Record Room, Gaoqing Country People’s Hospital, Zibo 256300, China