1. Department of Obstetrics, The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an 271000, Shandong, China
2. Department of Cardiology, The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an 271000, Shandong, China
3. Department of Geriatrics, The Affiliated Tai’an City Central Hospital of Qingdao University, Tai’an 271000, Shandong, China
4. Department of Internal Medicine, The Fourth People's Hospital of Tai’an City, Tai’an 271000, Shandong, China
5. Department of Obstetrics, Tai’an Maternal and Child Health Care Hospital, Tai’an 271000, Shandong, China