Early Postnatal Growth Predictors of Catch-Up Growth in Term Small-for-Gestational-Age Infants: A Nationwide Propensity-Score–Matched Study

Abstract

Background: Infants born small for gestational age (SGA) are at risk for impaired growth and metabolic complications. However, the long-term effects of early feeding type on catch-up growth (CUG) in SGA infants remain controversial, and there have been no established anthropometric thresholds to predict later CUG. Methods: This population-based study analyzed full-term SGA infants (birth weight <3rd percentile) from the Korean National Health Screening Program (2007-2014). Feeding type was classified as exclusively breastfeeding or exclusively formula-feeding based on consistent parent-reported data through the first year. Infants receiving mixed breast-and formula-feeding or special formulas were excluded to ensure a clear comparison between distinct feeding modalities. CUG was defined as height > 3rd percentile by 42–48 months. Propensity-score matching (1:1) was applied for sex, birth weight, socioeconomic status, and residence. Results: After 1:1 propensity-score matching, a final cohort of 1,832 infants was analyzed. Formula-fed infants exhibited faster early growth, but intergroup differences diminished after 9-12 months, resulting in comparable CUG rates at four years of age. Feeding type was not significantly associated with CUG (adjusted odds ratio 1.38; 95% CI 0.76–2.51). In contrast, weight and height Z-scores at 4–6 months independently predicted later CUG (AUC 0.77 and 0.84, respectively). Conclusion: Early weight-and height-for-age Z-scores at 4–6 months are the key determinant of CUG at 4 years of age in term SGA infants. Despite slower initial growth, breastfeeding supports equivalent long-term outcomes and may represent a physiologically favorable trajectory. Growth monitoring at 4–6 months may help identify infants at risk of persistent growth failure and provide a basis for considering timely nutritional support.