[1] China Med Univ, Dept Obstet & Gynecol, Shengjing Hosp, Shenyang 110004, Peoples R China
[2] Natl Res Inst Family Planning, Beijing 100081, Peoples R China
[3] Peking Union Med Coll, Grad Sch, Beijing 100021, Peoples R China
[4] HeNan Prov Res Inst Populat & Family Planning, Zhengzhou, Peoples R China
[5] Lanzhou Univ, Hosp 2, Lanzhou 730000, Peoples R China
[6] China Med Univ, Expt Res Ctr, Shengjing Hosp, Shenyang 110004, Peoples R China
[7] World Hlth Org Collaborating Ctr Res Human Reprod, Beijing, Peoples R China