Long-term growth effects of post-discharge formula in moderate-to-late preterm infants: follow-up at 24 months corrected age of a randomized controlled trial

Background: Moderate-to-late preterm (MLP) infants (i.e., <37 weeks’ gestation) are at risk for suboptimal neonatal nutrition and growth. We compared anthropometry and body composition at 24 months corrected age (CA; i.e., after term equivalent age (TEA)) between MLP infants fed either an isocaloric, protein- and mineral-enriched post-discharge formula (PDF) or standard term formula (STF) between TEA and 6 months CA. Methods: After enrollment (≤7 d postpartum), MLP infants received PDF if (fortified) mother’s own milk was insufficient. At TEA, those receiving >25% of intake as formula were randomized to either continue the same PDF or switch to STF until 6 months CA. At 24 months CA, anthropometry was assessed and air-displacement plethysmography was used to estimate body composition. Results: From the original study (n = 157), only 64 infants had anthropometry assessed and 34 infants had body composition estimated at 24 months CA. At the follow-up visit, PDF-fed infants had slightly larger head circumference compared to STF-fed infants (49.0 ± 1.5 and 48.3 ± 1.5 cm, p < 0.05). Despite similar total body weight at 24 months CA, PDF-fed infants had lower fat mass and higher fat-free mass compared to STF-fed infants (fat mass: 2392 ± 923 and 3615 ± 1359 g; fat-free mass: 10461 ± 1030 and 10108 ± 1700 g; respectively, p < 0.05). Conclusions: Providing MLP infants with PDF for 6 months after TEA was associated with lower fat mass and higher fat-free mass, with similar bodyweights at 24 months CA compared to those fed STF. Our findings should be interpreted cautiously, due to high loss-to-follow-up.