1. Nuffield Department of Obstetrics and Gynaecology; University of Oxford; Oxford Radcliffe Hospitals NHS Trust; Oxford UK
2. Clinical Sciences Research Institute; Warwick Medical School; Coventry UK
3. School of Clinical and Experimental Medicine (Reproduction, Genes and Development); College of Medical and Dental Sciences; University of Birmingham; Birmingham UK
4. Women's Health Research Unit; Centre for Primary Care and Public Health; Barts and the London School of Medicine and Dentistry; Queen Mary University of London; London UK