1. Department of Obstetrics and Gynecology, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China;
2. Department of Obstetrics and Gynecology, Jiaxing Maternity and Child Health Care Hospital, Jiaxing, China;
3. Department of Obstetrics and Gynecology, The Second Hospital of Hebei Medical University, Hebei, China