[1] Univ Oxford, Coll 1Balliol, Oxford OX2 6GG, England
[2] Lister Hosp, Stevenage, Herts, England
[3] Sheffield Teaching Hosp NHS Fdn Trust, Sheffield, S Yorkshire, England
[4] UCL Med Sch, Dept Primary Care & Populat Hlth, London, England
[5] Hosp Ramon & Cajal, Clin Biostat Unit, E-28034 Madrid, Spain
[6] Homerton Univ Hosp NHS Fdn Trust, Dept Obstet & Gynaecol, London, England
[7] Barts & London Queen Marys Sch Med & Dent, Inst Hlth Sci Educ, Clin & Commun Skills Learning Unit, London, England
[8] Univ Auckland, Cochrane Menstrual Disorders & Subfertil Grp, Auckland 1, New Zealand
[9] Cardiff Univ, Inst Med Educ, Cardiff CF10 3AX, S Glam, Wales
[10] Univ London, Womens Hlth Res Unit, London, England