[1] Sichuan Univ, West China Sch Publ Hlth, Dept Epidemiol & Biostat, Chengdu, Sichuan, Peoples R China
[2] Sichuan Univ, Key Lab Birth Defects & Related Dis Women & Child, Chengdu, Sichuan, Peoples R China
[3] Chengdu Municipal Ctr Dis Control & Prevent, Chengdu, Sichuan, Peoples R China