1. School of Public Health Zhejiang Chinese Medical University Hangzhou China
2. Department of Public Health, Faculty of Medicine University of Helsinki Helsinki Finland
3. Division of Obstetrics & Gynecology, Department of Clinical Science, Intervention and Technology (CLINTEC) Karolinska Institutet Stockholm Sweden
4. Department of Clinical Medicine UiT The Arctic University of Tromsø Tromsø Norway
5. Department of Obstetrics and Gynecology The First Affiliated Hospital of University of Science and Technology of China (USTC) Hefei China
6. Medical Teaching and Research Section Anhui Open University Hefei China