1. Department of Obstetrics and Gynecology, Shengjing Hospital Affiliated to China Medical University, Shenyang, Liaoning, China
2. Department of Obstetrics and Gynecology, Hospital of Zhengzhou University, Zhengzhou, Henan, China
3. Department of Obstetrics and Gynecology, Beijing Chaoyang Hospital Affiliated to Capital Medical University, Beijing, China