Table 1.

Collected variables and definitions

Perinatal variables	Postnatal variables
Delivery mode (i.e., vaginal or caesarian section)	Gestational age
Single or multiple births	Birthweight
Preterm premature rupture of membranes (i.e., ≥24 h before delivery)	Apgarscore
Meconium-stained amniotic fluid	Patent ductus arteriosus
	Medication
	Antibiotics 1 Total duration of treatment (days) 2 Duration of antibiotic treatment initiated within 24 h postnatally (0, 1–3, or >3 days) 3 Antibiotic exposure (yes/no)
	Ventilation mode
	Diagnosis of necrotizing enterocolitis
	Diagnosis of spontaneous intestinal perforation
	Diagnosis of sepsis, including the causative pathogen: 1 Gram-positive bacteria (including CoNS) 2 Gram-negative bacteria 3 Fungi 4 CoNS
	Number of red blood cell transfusions
	Central (umbilical line and/or peripherally inserted central catheter) and peripheral venous catheter use: 1 Cumulative number of days a certain line was present 2 Presence of a line within 48 h prior to LOS onset
	Parenteral feeding practices (lipids or amino acids)
	Enteral feeding practices 1 Breast-fed, defined as the daily average enteral feeding volume consisting of >80% breastmilk, including donor milk 2 Formula-fed, defined as the daily average enteral feeding volume consisting of >50% formula 3 Combination of breastmilk and formula, that encompasses infants not meeting the criteria for (1) and (2)
	Time to full enteral feeding, defined as at least 2 consecutive days without additional parenteral feeding administration
	Radiologic results (i.e., abdominal radiography)
	Laboratory results (i.e., C-reactive protein and blood cultures)