1. Department of Obstetrics and Gynecology, Peking Union Medical College Hospital Chinese Academy of Medical Sciences, Peking Union Medical College, National Clinical Research Center for Obstetric and Gynecologic Diseases Beijing China
2. Department of Ultrasonic Diagnosis, Peking Union Medical College Hospital Chinese Academy of Medical Sciences Beijing China
3. Department of Obstetrics and Gynecology General Hospital of Northern Theater Command Shenyang Liaoning Province China
4. Department of Obstetrics and Gynecology Beijing Daxing People's Hospital Beijing China
5. Department of Obstetrics and Gynecology Tongzhou Maternal and Child Health Hospital of Beijing Beijing China
6. Department of Obstetrics and Gynecology Beijing Shunyi District Maternal and Child Health Hospital Beijing China