[1] Univ Ghent, Int Ctr Reprod Hlth, Ghent, Belgium
[2] Univ Libre Bruxelles, Fac Med, Res Lab Human Reprod, Brussels, Belgium
[3] Aarhus Univ, Dept Clin Epidemiol, Aarhus, Denmark
[4] Shanghai Inst Planned Parenthood Res, Shanghai, Peoples R China
[5] Chinese Med Assoc, Chinese Soc Family Planning, Beijing, Peoples R China
[6] Natl Res Inst Family Planning, Beijing, Peoples R China
[7] Fudan Univ, Sch Publ Hlth, Shanghai, Peoples R China
[8] Chongqing Med Univ, Dept Obstet & Gynecol, Affiliated Hosp 2, Chongqing, Peoples R China
[9] Chengde Nursing Vocat Coll, Chengde, Peoples R China
[10] Univ Liverpool Liverpool Sch Trop Med, Liverpool, Merseyside, England