1 University of Edinburgh Division of Reproductive and Developmental Sciences, Simpson Centre for Reproductive Health, Royal Infirmary of Edinburgh, Scotland (Stock) Department of Radiology, Simpson Centre for Reproductive Health, Royal Infirmary of Edinburgh, Scotland (Walker) Department of Obstetrics, Simpson Centre for Reproductive Health, Royal Infirmary of Edinburgh, Scotland (Cooper) University of Edinburgh Division of Reproductive and Developmental Sciences, Simpson Centre for Reproductive Health, Royal Infirmary of Edinburgh, Scotland (Norman).