1 Neonatal Intensive Care Unit, Hospital São João, Porto, Portugal. Electronic address: gusrocha@sapo.pt.
2 Neonatal Intensive Care Unit, Hospital São João, Porto, Portugal; Faculty of Medicine, University of Porto, Porto, Portugal.
3 Faculty of Medicine, University of Porto, Porto, Portugal; Department of Pediatrics, Centro Hospitalar São João, Porto, Portugal; EpicUnit, Institute of Public Health, University of Porto, Porto, Portugal.