The objective was to explore the association between antibiotic use in the first 72 h of life in low risk for infection preterm infants and nutritional performance.

Among the 4344 children born between 2010 and 2012 in 16 centres of the BNNR weighing <1495 g, 2395 infants presented no maternal history of chorioamnionitis, <18 h of ruptured membranes, no diagnosis of sepsis in the first 72 h of life and no congenital malformations. Antibiotics were given to 959 infants during the first 72 h of life and 1436 received no antibiotics.

The use of antibiotic was more frequent among children with worst birth conditions and those infants presented poorer evolution parameters except for lower incidence of late onset sepsis.

In nutritional terms, after binary logistic regression (BLR), the use of antibiotics remained as independent risk factors to take over 14 days to regain birth weight and for having lost more than 1 z-score in weight at discharge.

Centres were stratified by the percentage of antibiotic use. Prenatal and birth condition of the two centres strata were very similar. Infants from Conservative centres presented better nutritional performance, but higher incidence of late onset sepsis, use of antibiotics after 72 hs, more days of oxygen use.

At BLR for use of oxygen at 36 CA, neither centre strata, nor use of antibiotics during the first 72 hs of life maintained the association found on the univariate analysis.

The use of antibiotics in the first 72 h was independently associated with worse nutritional performance.