Rachel L Knowles1, Deborah Ridout2, Sonya Crowe3, Catherine Bull4, Jo Wray5, Jenifer Tregay6, Rodney C G Franklin7, David J Barron8, Roger C Parslow9, Katherine Brown10. 1. Life Course Epidemiology & Biostatistics, UCL Great Ormond Street Institute of Child Health, London, UK. 2. Population Policy and Practice Programme, UCL Great Ormond Street Institute of Child Health, London, UK. 3. Clinical Operational Research Unit, University College London, London, UK. 4. Department of Cardiology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK. 5. Centre for Outcomes and Experience Research in Children's Health Illness and Disability, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK. 6. Department of Clinical Psychology, John Radcliffe Hospital, Oxford, Oxfordshire, UK. 7. Department of Paediatric Cardiology, Royal Brompton and Harefield NHS Trust, London, UK. 8. Department of Paediatric Cardiac Surgery, Birmingham Children's Hospital NHS Foundation Trust, Birmingham, UK. 9. Paediatric Epidemiology Group, University of Leeds, Leeds, UK. 10. Cardiac Intensive Care Unit, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK.