1. Department of Nursing The Seventh Affiliated Hospital of Southern Medical University Foshan Guangdong China
2. Department of Obstetrics The Seventh Affiliated Hospital of Southern Medical University Foshan Guangdong China
3. Ottawa Hospital Research Institute Ottawa Ontario Canada
4. Department of Obstetrics & Gynecology University of Ottawa Faculty of Medicine Ottawa Ontario Canada
5. School of Epidemiology and Public Health University of Ottawa Faculty of Medicine Ottawa Ontario Canada