MRC Lifecourse Epidemiology Unit, University of Southampton, UK. Institute of Developmental Sciences, University of Southampton, UK. Paediatric Endocrinology, University Hospitals Southampton NHS Foundation Trust, Southampton, UK. Academic Unit of Child Health, Sheffield Children's Hospital, University of Sheffield, Sheffield, UK. Nuffield Department of Obstetrics and Gynaecology, John Radcliffe Hospital, University of Oxford, Oxford, UK. MRC Elsie Widdowson Laboratory, Cambridge, UK. Department of Medicine, Faculty of Medicine and Health Sciences, University of East Anglia, Norwich, UK. Sheffield Hospitals NHS Trust, (University of Sheffield), Sheffield, UK. NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, UK. NIHR Southampton Biomedical Research Centre, University of Southampton and University Hospital Southampton NHS Foundation Trust, Southampton, UK.