1. Department of Obstetrics and Gynecology, Hospital Universitario Miguel Servet, Zaragoza, Spain
2. Department of Obstetrics and Gynecology, Hospital Universitario General de Villalba, Madrid, Spain
3. Escuela Universitaria Politécnica de la Almunia, Universidad de Zaragoza, Zaragoza, Spain
4. Department of Obstetrics and Gynecology, Hospital Universitario Gregorio Marañón, Madrid, Spain
5. Department of Obstetrics and Gynecology, San Pedro Hospital, Logroño, La Rioja, Spain