[1] Barts Hlth NHS Trust, London, England
[2] NHS Blood & Transplant, London, England
[3] Univ Oxford, Natl Perinatal Epidemiol Unit, Oxford OX1 2JD, England
[4] NHS Blood & Transplant, Stat & Clin Studies, Bristol, Avon, England
[5] Cardiff Univ, Arthur Bloom Haemophilia Ctr, Cardiff CF10 3AX, S Glam, Wales
[6] Cardiff & Vale Univ Hlth Board, Dept Anaesthet, Cardiff, S Glam, Wales
[7] Univ Liverpool, Dept Womens & Childrens Hlth, Liverpool L69 3BX, Merseyside, England
[8] Univ Leeds, Dept Womens & Childrens, Leeds LS2 9JT, W Yorkshire, England
[9] NHS Blood & Transplant, Oxford, England
[10] Oxford Univ Hosp NHS Trust, Oxford, England