1. London School of Hygiene & Tropical Medicine; Clinical Trials Unit; Keppel Street London UK WC1E 7HT
2. Oxford University Hospitals, John Radcliffe Hospital; Clinical Haematology; Oxford UK OX3 9DU
3. University Hospitals of Geneva; Division of Clinical Epidemiology, Medical Directorate; Geneva Switzerland
4. Leicester Royal Infirmary; University Department of Obstetrics and Gynaecology, Fetal and Maternal Medicine Unit; Infirmary Square Leicester UK LE1 5WW