1. Department of Obstetrics and Gynecology, Shengjing Hospital of China Medical University, Shenyang, China
2. The Third People’s Hospital of Liaoyang City, Liaoyang, China
3. Department of Gynecology, Liaoning Cancer Hospital, Shenyang, China
4. Department of Obstetrics & Gynecology, Beijing Chao-Yang Hospital Affiliated to Capital Medical University, Beijing, China
5. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
6. Department of Obstetrics and Gynecology, China General Hospital of Shenyang Military Region, Shenyang, China