1 Department of Obstetrics and Gynaecology, Queen Mary Hospital, University of Hong Kong, Hong Kong SAR, China. Electronic address: kelvincheung82@hotmail.com.
2 Department of Obstetrics and Gynaecology, Queen Mary Hospital, University of Hong Kong, Hong Kong SAR, China.
3 The Fetal Medicine Centre, Birmingham Women's and Children's Foundation Trust, Edgbaston, Birmingham, UK; The Institute of Metabolism and Systems Research, College of Medical & Dental Sciences, University of Birmingham, Birmingham, UK.