1. Department of Obstetrics and Gynecology, Guiyang Maternity and Child Health Care Hospital, Guizhou 550003, People’s Republic of China
2. Department of Obstetrics and Gynecology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Hubei 430030, People’s Republic of China
3. Department of Obstetrics and Gynecology, China-Japan Friendship Hospital, Beijing 100029, People’s Republic of China
4. Department of Obstetrics and Gynecology, The Affiliated Hospital of Guizhou Medical University, Guizhou 550025, People’s Republic of China