[1] Peking Univ First Hosp, Dept Obstet & Gynecol, 1 Xianmen St, Beijing 100034, Peoples R China
[2] Chinese Ctr Dis Control & Prevent, Natl Ctr Chron & Noncommunicable Dis Control & Pr, Beijing, Peoples R China
[3] Chinese Ctr Dis Control & Prevent, Natl Ctr Women & Childrens Hlth, Beijing, Peoples R China