[1] Univ Amsterdam, Amsterdam Reprod & Dev Inst, Dept Obstet & Gynaecol, Amsterdam UMC, Meibergdreef 9, Amsterdam, Netherlands
[2] Tergooi Med Ctr, Dept Obstet & Gynaecol, Hilversum, Netherlands
[3] Epsom & St Helier Univ Hosp, Beginnings Assisted Concept Unit, London, England
[4] UCL, Inst Clin Trials & Methodol, Comprehens Clin Trials Unit, London, England
[5] Univ Granada, Dept Prevent Med & Publ Hlth, Granada, Spain
[6] Consortium Biomed Res Epidemiol & Publ Hlth CIBERE, Granada, Spain