1. School of Basic Medicine, Qingdao Medical College, Qingdao, University, Qingdao 266071, China
2. Department of Obstetrics and Gynecology, The Affiliated Qingdao Municipal Hospital of Qingdao University, Qingdao, 266000, China
3. Department of Obstetrics, Qingdao Municipal Hospital, Qingdao, 266000, China