1. Reproduction Unit Cruces Hospital Biocruces Health Research InstituteBIOEF Vizcaya Spain
2. Department of Gynecology and Obstetrics Faculty of Medicine and Nursing University of the Basque Country Vizcaya Spain
3. IVI Bilbao Vizcaya Spain
4. Clinical Epidemiological Unit Cruces Hospital Biocruces Health Research InstituteBIOEF Vizcaya Spain
5. Department of Mathematics Faculty of Science and Technology University of the Basque Country Vizcaya Spain