1. Department of Obstetrics and Gynecology Valme University Hospital Seville Spain
2. Department of Obstetrics and Gynecology, Faculty of Medicine University of Seville Seville Spain
3. Department of Obstetrics and Gynecology University Healthcare Complex of Gran Canaria Gran Canaria Spain
4. Obstetrics and Gynecology Department Juan Ramon Jiménez Hospital Huelva Spain
5. Department of Obstetrics and Gynecology University Healthcare Complex of Leon (CAULE) Leon Spain
6. Department of Obstetrics and Gynecology Virgen de la Victoria University Hospital of Malaga Malaga Spain
7. Department of statistics and operational research University of Cadiz Cadiz Spain