1. National Office for Maternal and Child Health Surveillance of China, Department of Obstetrics, West China Second University Hospital, Sichuan University, Chengdu, China.
2. Key Laboratory of Birth Defects and Related Diseases of Women and Children (Sichuan University), Ministry of Education, Chengdu, China.
3. National Office for Maternal and Child Health Surveillance of China, Department of Paediatrics, West China Second University Hospital, Sichuan University, Chengdu, China.