1. Obstetrics and Gynecology Department, Biocruces Bizkaia Health Research Institute, Cruces University Hospital, Bizkaia, Spain;
2. Clinical Epidemiology Unit, Biocruces Bizkaia Health Research Institute, Cruces University Hospital, Bizkaia, Spain;
3. CIBER Epidemiology and Public Health (CIBERESP), Spanish Clinical Research Network (SCReN), Madrid, Spain;
4. Anesthesia Department, Biocruces Bizkaia Health Research Institute, Cruces University Hospital, Bizkaia, Spain