1. Department of Emergency, Qilu Hospital of Shandong University, Jinan, China
2. Department of Gynaecology and Obstetrics, Qilu Hospital Affiliated to Shandong University, Jinan, China
3. Department of Obstetrics and Gynecology, Jinan maternity and child care hospital, Jinan, China
4. Department of Physiology, Medicine School of Shandong University, Jinan, China
5. Department of Obstetrics and Gynecology, Second Hospital of Shandong University, Jinan, China