1. Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China
2. National Centre for Healthcare Quality Management in Obstetrics, Peking University Third Hospital, Beijing, China
3. National Clinical Research Centre for Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China
4. Institute of Reproductive and Child Health, Peking University Health Science Centre, Beijing, China
5. National Health Commission Key Laboratory of Reproductive Health, Peking University Health Science Centre, Beijing, China
6. Department of Obstetrics and Gynecology, the Third Affiliated Hospital of Guangzhou Medical University, Guangzhou, China