1. Department of Women and Children Health, Xiangya School of Public Health, Central South University, Changsha, Hunan Province, China
2. Department of Social Medicine and Health Management, Xiangya School of Public Health, Central South University, Changsha, Hunan Province, China
3. Department of Women Health Care, Hunan Provincial Maternal and Child Health Care Hospital, Changsha, Hunan Province, China
4. Department of Epidemiology, Xiangya School of Public Health, Central South University, Changsha, Hunan Province, China