1. Department of Social Medicine and Health Education, School of Public Health, Peking University Health Science Center, Beijing 100191, China
2. School of Public Health, Sichuan University, Chengdu 610041, China
3. Department of Pediatrics, Peking University Third Hospital, Beijing 100191, China
4. Obstetrics Department, Maternal and Child Hospital of Haidian District, Beijing 100080, China
5. Institute of Biotechnology and Health, Beijing Academy of Science and Technology, Beijing 100089, China