1. Department of Obstetrics, The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an, 271000 Shandong Province, China
2. Department of Stomatology, The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an, 271000 Shandong Province, China
3. Department of Obstetric and Gynecologic Ultrasound, The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an, 271000 Shandong Province, China
4. Department of Geriatrics, The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an, 271000 Shandong Province, China