[1] Shanghai Jiao Tong Univ, Sch Med, Xinhua Hosp, Dept Obstet, Shanghai, Peoples R China
[2] Univ Ottawa, Dept Obstet & Gynecol, OMNI Res Grp, Fac Med, Ottawa, ON, Canada
[3] Ottawa Hosp Res Inst, Clin Epidemiol Program, Ottawa, ON, Canada
[4] Capital Med Univ, Beijing Friendship Hosp, Dept Obstet & Gynecol, Beijing, Peoples R China
[5] Cent S Univ, Sch Publ Hlth, Changsha, Hunan, Peoples R China
[6] Canadian Agcy Drugs & Technol Hlth, Ottawa, ON, Canada
[7] Univ Ottawa, Fac Med, Sch Epidemiol Publ Hlth & Prevent Med, Ottawa, ON, Canada