1. Department of Women's and Children's Health, Institute of Translational Medicine; University of Liverpool; Liverpool; UK
2. Department of Obstetrics and Gynecology, Maternal-Fetal Medicine Division; University of Alabama; Birmingham; AL; USA
3. Maternal Fetal Medicine Unit, Department of Obstetrics, Hospital Universitari Vall d'Hebron; Universitat Autonoma de Barcelona; Barcelona; Spain
4. Department of Biostatistics; University of Alabama; Birmingham; AL; USA