[1] Guys & St Thomas NHS Fdn Trust, Dept Womens Hlth, London, England
[2] Kings Coll London, Dept Womens Hlth, London, England
[3] Univ Oxford, Hosp NHS Fdn Trust, Dept Haematol, Oxford, England
[4] Barking Havering & Redbridge Univ Hosp, Dept Obstet & Gynaecol, Romford, Essex, England
[5] London Sch Hyg & Trop Med, London, England
[6] Norwegian Inst Publ Hlth, Ctr Fertil & Hlth, Oslo, Norway
[7] Birmingham Hosp NHS Trust, Dept Haematol, Sandwell & West, London, North Ireland
[8] Guys & St Thomas NHS Fdn Trust, Dept Haematol, London, England
[9] Kings Coll London, Dept Haematol, London, England