[1] Peking Univ, Sch Publ Hlth, Dept Maternal & Child Hlth, Beijing 100191, Peoples R China
[2] Chinese Acad Med Sci & Peking Union Med Coll, Fuwai Hosp, Dept Epidemiol, Beijing 100037, Peoples R China
[3] Peking Univ Third Hosp, Dept Obstet & Gynecol, 49 North Garden Rd, Beijing 100191, Peoples R China
[4] Peking Univ, Inst Reprod & Child Hlth, Key Lab Reprod Hlth, Natl Hlth Commiss Peoples Republ China, Beijing 100191, Peoples R China
[5] Peking Univ, Sch Publ Hlth, Dept Maternal & Child Hlth, 38 Xueyuan Rd, Beijing 100191, Peoples R China