Postnatal Growth Patterns and Deviations in Singleton and Twin Infants: A Prospective Cohort Study on Infants Appropriate and Small for Gestational Age

Small for gestational age (SGA) and twin infants are at increased risk of growth deviations, but postnatal catch-up growth (CUG) patterns across singleton, twin, appropriate for gestational age (AGA), and SGA groups remain unclear. This prospective cohort study (<i>n</i> = 340) investigated the postnatal growth trajectories and physical growth deviations in singleton and twin AGA and SGA infants during the first year of life. The primary findings indicated that SGA infants exhibited rapid CUG in weight and head circumference within the first 6 months, whereas length catch-up required a longer period. Twin SGA infants displayed distinct patterns: faster weight CUG but slower length CUG compared with singleton SGA infants, with gender differences-male SGA twins had lower length <i>z</i>-scores than SGA singletons. The rate of deviation in physical growth of SGA infants improved significantly within the first year of life, with wasting being infrequent. In conclusion, the mechanism underlying SGA is more complex among twins than singletons. Twin SGA infants require prolonged growth monitoring, and regular follow-up is essential to optimize growth outcomes and mitigate long-term risks. This preliminary study offers a foundation for further investigation into the biological and environmental factors driving these differences.