1. Department of Obstetrics and Gynecology, Hospital de Cruces, País Vasco University, Baracaldo, Vizcaya, Spain,
2. Department of Obstetrics and Gynecology, Hospital de Cruces, País Vasco University, Baracaldo, Vizcaya, Spain
3. Department of Obstetrics and Gynecology, University Hospital `Príncipe de Asturias', Alcalá de Henares, Madrid, Spain