1. Department of Gynecology and Obstetrics, Yantai Yuhuangding Hospital, Affiliated to Qingdao University, Yantai, Shandong 264000, P.R. China
2. Department of Cardiology, Yantai Yuhuangding Hospital, Affiliated to Qingdao University, Yantai, Shandong 264000, P.R. China
3. Department of Gynecology and Obstetrics, Tianjin Medical University General Hospital, Tianjin 300052, P.R. China