1. Fetal Medicine Research Institute; King's College Hospital; London UK
2. Obstetrics and Gynecology Department; Torrejon University Hospital, Torrejon de Ardoz; Madrid Spain
3. Obstetrics and Gynecology Department; Universidad Francisco de Vitoria, Pozuelo de Alarcón; Madrid Spain
4. Clinical Biostatistics Unit, Ramón y Cajal Hospital (IRYCIS); CIBER Epidemiology and Public Health (CIBERESP); Madrid Spain