[1] St Marys Hosp, Manchester, Lancs, England
[2] Imperial Coll Healthcare Trust, Queen Charlottes & Chelsea Hosp, London, England
[3] Univ Nottingham, Sch Med, Div Child Hlth Obstet & Gynaecol, Nottingham, England
[4] Royal Derby Hosp, Fertil Unit, Derby, England
[5] Univ Warwick, Clin Sci Res Inst, Coventry CV4 7AL, W Midlands, England
[6] Univ Auckland, Cochrane Off, Auckland 1, New Zealand