Behavior of weight z-score in preterm infants who are small for gestational age.

Introduction: the follow-up of small for gestational age (SGA) preterm infants is critical due to their differentiated postnatal growth pattern. Objective: to investigate the weight z-score behavior in SGA preterm infants during a four-week stay in a Neonatal Intensive Care Unit. Methods: a retrospective longitudinal study with data from nutritional anamneses of 190 preterm infants admitted to a Neonatal Intensive Care Unit between January/2017 and December/2019, classified according to nutritional status at birth as either SGA or appropriate for gestational age (AGA). Linear regression was used to verify association between weight z-score with gestational age, birth weight, initiation of enteral nutrition and relative amount of energy and protein administered. Results: SGA preterm infants accounted for 23 % of the study participants. In SGA, the difference in weight score was observed at week 1 when compared to admission (p < 0.05), while in AGA there was a difference sustained during the whole period (p < 0.05). In SGA, the linear regression analysis showed that the change in z-score was explained by time to start of enteral nutrition (p = 0.033), gestational age (p = 0.003) and birth weight (p = 0.001). In AGA the change was explained by gestational age (p = 0.000) and birth weight (p = 0.000). Conclusion: the weight z-score behavior in preterm infants was downward compared to admission, stable at the end of 4 weeks, and different according to nutritional status at birth. In the AGA group the decline in nutritional status was not recovered throughout hospitalization and in the SGA group the unfavorable nutritional status was maintained.