1. Department of Obstetrics and GynecologyValme University Hospital Seville Spain
2. Department of Obstetrics and GynecologyUniversity of Seville Seville Spain
3. Department of Obstetrics and GynecologyComplejo Asistencial Universitario de Gran Canarias Gran Canarias Spain
4. Department of Obstetrics and GynecologyComplejo Asistencial Universitario de Leon (CAULE) Leon Spain
5. Biostatistics Unit, Department of Preventive Medicine and Public HealthUniversity of Seville Seville Spain