1 Fetal Medicine Unit, Department of Obstetrics and Gynecology, St George's University Hospital, University of London, London, England, United Kingdom.
2 Department of Obstetrics and Gynecology, Koc University Hospital, Istanbul, Turkey.
3 Fetal Medicine Unit, Department of Obstetrics and Gynecology, St George's University Hospital, University of London, London, England, United Kingdom; Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's University Hospital, London, United Kingdom; Twin and Multiple Pregnancy Centre for Research and Clinical Excellence, St George's University Hospital, St George's University of London, London, United Kingdom; Fetal Medicine Unit, Liverpool Women's Hospital, Liverpool, United Kingdom. Electronic address: akhalil@sgul.ac.uk.