Calorie intake is associated with weight gain during transition phase of nutrition in female extremely low birth weight infants.

We sought to determine whether there are sex-based differences in the requirements for calories or protein for optimal growth during the transition phase (TP) when an extremely low birth weight (ELBW) infant, defined as a preterm infant with a birth weight of < 1000 g, is progressing from parenteral to enteral feeds. A retrospective review of ELBW infants born from 2014 to 2016 was performed at a tertiary NICU. Infants with necrotizing enterocolitis, short bowel syndrome, or chromosomal anomalies were excluded. TP was defined as the period when the infant's enteral feeds were increased from 30 up to 120 ml/kg/day while weaning parenteral nutrition (PN). Effects of sex and protein-calorie intake on the change in growth parameters from the beginning to the end of TP were analyzed. Pre-TP growth percentiles and calorie and protein intake were similar in both sexes. There was a significant (r = 0.22, p = 0.026) correlation of total calorie intake with a change in weight percentiles (wt.pc) for the whole group, but on sex-specific analysis, this correlation was more robust and significant only in girls (r = 0.28, p = 0.015). Protein intake did not correlate with the changes in wt.pc in either sex. Despite a similar intake of calories and protein during the TP, we found a significant decrease in wt.pc only in girls. More extensive studies are needed to understand the sex-based differences in caloric needs and metabolic rate in ELBW infants.