Oxford handbook of obstetrics and gynaecology / edited by Sally Collins (Consultant Obstetrician and Subspecialist in Maternal and Fetal Medicine, John Radcliffe Hospital, Oxford, and Professor of Obstetrics, Nuffield Department of Women's and Reproductive Health, University of Oxford, Oxford, UK), Sabaratnam Arulkumaran (Professor of Obstetrics and Gynaecology, University of Nicosia Medical School, Cyprus, Professor Emeritus, St. George's, University of London, and Visiting Professor, Imperial College London, London, UK), Kevin Hayes (Consultant Obstetrician and Gynaecologist, St. George's University Hospital NHS Foundation Trust, London, UK), Kirana Arambage (Consultant Gynaecologist, John Radcliffe Hospital, Oxford, and Honorary Senior Clinical Lecturer, Nuffield Department of Women's and Reproductive Health, University of Oxford, Oxford, UK), Lawrence Impey (Consultant Obstetrician and Subspecialist in Maternal and Fetal Medicine, John Radcliffe Hospital, Oxford, UK).