[1] Guangxi Med Univ, Sch Publ Hlth, Dept Epidemiol & Hlth Stat, 22 Shuangyong Rd, Nanning 530021, Guangxi, Peoples R China
[2] Nanning Wuming Dist Maternal & Child Hlth Care Hos, Nanning 530100, Guangxi, Peoples R China
[3] Guangxi Med Univ, Affiliated Hosp 3, Dept Obstet, Nanning 530031, Guangxi, Peoples R China
[4] Guangxi Med Univ, Sch Publ Hlth, Dept Sanit Chem, Nanning 530021, Guangxi, Peoples R China
[5] Guangxi Med Univ, Sch Publ Hlth, Dept Maternal Child & Adolescent Hlth, Nanning 530021, Guangxi, Peoples R China