1. Obstetrics and Gynecology Service; BioCruces Health Research Institute; Cruces University Hospital (UPV/EHU); Barakaldo Spain
2. Clinical Epidemiology Unit; BioCruces Health Research Institute; Cruces University Hospital (UPV/EHU); Barakaldo Spain
3. Spanish Clinical Research Network (SCReN); Madrid Spain
4. CIBER de Epidemiología y Salud Pública (CIBERESP); Madrid Spain
5. Anesthesia Service; BioCruces Health Research Institute; Cruces University Hospital (UPV/EHU); Barakaldo Spain