1. Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China
2. National Clinical Research Centre for Obstetrics and Gynaecology, Beijing, China
3. National Centre for Healthcare Quality Management in Obstetrics, Beijing, China
4. Institute of Reproductive and Child Health, National Health Commission Key Laboratory of Reproductive Health, Peking University Health Science Centre, Beijing, China
5. Department of Obstetrics, Women and Children’s Hospital of Chongqing Medical University, Chongqing, China
6. Department of Healthcare Quality Evaluation, Bureau of Medical Administration, National Health Commission of the People’s Republic of China, Beijing, China