1. Department of Gynecology and Obstetrics, Qilu Hospital of Shandong University, Jinan, Shandong 250012, P.R. China
2. Electrocardiogram Room, Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, Shandong 264000, P.R. China
3. Reproductive Medicine Center, Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, Shandong 264000, P.R. China
4. Department of Gynecology, Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, Shandong 264000, P.R. China