1. Pediatric Service, Neonatology Unit, Puerta de Hierro-Majadahonda University Hospital, Universidad Autónoma de Madrid, Majadahonda, Madrid, Spain
2. Pediatric Service, Neonatology Unit, Severo Ochoa University Hospital, Leganés, Madrid, Spain
3. Pediatric Service, Neonatology Unit, Príncipe de Asturias University Hospital, Universidad de Alcalá de Henares, Madrid, Spain
4. Pediatric Service, Neonatology Unit, Getafe University Hospital, Getafe, Madrid, Spain
5. Pediatric Service, Neonatology Unit, Fuenlabrada University Hospital, Fuenlabrada, Madrid, Spain
6. Biostatistics Unit, Puerta de Hierro Biomedical Research Institute, CIBERESP, Madrid, Spain
7. Pediatric Service, Puerta de Hierro-Majadahonda University Hospital, Universidad Autónoma de Madrid, Majadahonda, Madrid, Spain