[1] Royal Coll Obstet & Gynaecologists, Clin Qual, 10-18 Union St, London SE11GH, England
[2] Univ Bristol, Southmead Hosp, Musculoskeletal Res Unit, Level 1,Learning & Res Bldg, Bristol BS10 5NB, England
[3] Caribbean & African Hlth Network, Transformat Community Resource Ctr, 1st Floor,Richmond House,11 Richmond Grove, Manchester M13 0LN, England
[4] Queen Mary Univ London, Wolfson Inst Populat Hlth, Womens Hlth Res Unit, London, England