Montserrat Izquierdo1,2, Martín Iriondo1,2, César Ruiz2,3, Gonzalo Zeballos4,5, Miguel Sánchez6, Eva González7,8, Máximo Vento2,9, Marta Thió10,11,12. 1. Division of Neonatology, BCNatal Hospital Sant Joan de Déu-Hospital Clínic, Esplugues de Llobregat (Barcelona), Spain. 2. Maternal and Infant Health and Development Research Network SAMID (RD 12/0026/0002), Health Research Institute Carlos III, Spanish Ministry of Economy and Competitiveness, Barcelona, Spain. 3. Division of Neonatology, Hospital de la Vall d'Hebrón, Barcelona, Spain. 4. Division of Neonatology, Hospital General Universitario Gregorio Marañón, Madrid, Spain. 5. Health Research Institute Gregorio Marañón (IiSGM), CIBEREHD, Madrid, Spain. 6. Division of Neonatology, Hospital Puerta del Hierro, Majadahonda (Madrid), Spain. 7. Division of Neonatology, Hospital Alvaro Cunqueiro, Beade (Pontevedra), Spain. 8. Biomedical Research Institute University of Santiago de Compostela, La Coruña, Spain. 9. Division of Neonatology, Hospital Universitario y Politécnico La Fe, Valencia, Spain. 10. Department of Newborn Research, The Royal Women's Hospital, Melbourne, Victoria, Australia. 11. Department of Obstetrics and Gynaecology, The University of Melbourne, Melbourne, Victoria, Australia. 12. PIPER - Neonatal Retrieval Services, The Royal Children's Hospital, Melbourne, Victoria, Australia.