1. Department of Gynecology, Hebei Linxi People’s Hospital, Xingtai, Hebei, China (mainland)
2. Department of Ultrasound, The Second hospital of Hebei Medical University, Shijiazhuang, Hebei, China (mainland)
3. Department of Epidemiology and Statistics, School of Public Health, Hebei Medical University, Shijiazhuang, Hebei, China (mainland)
4. Department of Gynecology, The First hospital of Hebei Medical University, Shijiazhuang, Hebei, China (mainland)
5. Department of Epidemic Treatment and Prevention, Center for Disease Prevention and Control of Shijiazhuang City, Shijiazhuang, Hebei, China (mainland)