1. Hospital General Universitario Gregorio Marañón, Madrid, Spain
2. Department of Obstetricis, Miguel Servet University Hospital, Zaragoza, Spain
3. Department of Obstetrics and Gynecology, Hospital Universitario 12 de Octubre, Madrid, Spain
4. Hospital Sanitas La Zarzuela, Madrid, Spain
5. Universidad de Zaragoza, Escuela Universitaria Politécnica de la Almunia, C/Mayor s/n, La Almunia de Doña Godina, Spain
6. Villalba General Hospital, Collado Villalba, Spain
7. Obstetricia y Ginecología, Hospital San Pedro, Logrono, Spain