1. Women's Health Research Unit, Wolfson Institute of Population Health Queen Mary University of London London UK
2. Queen Mary University of London Medical School London UK
3. Imperial College NHS Healthcare Trust London UK
4. North West Anglia NHS Foundation Trust Peterborough UK
5. Centre for Reproductive and Genetic Health London UK
6. Hewitt Fertility Centre Liverpool Women's Hospital Liverpool UK
7. Department of Preventative Medicine and Public Health, Faculty of Medicine University of Granada Granada Spain
8. CIBER Epidemiology and Public Health Madrid Spain