Early postnatal growth predictors of catch-up growth in term small-for-gestational-age infants: a nationwide propensity-score–matched study

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.