Distinct birth size and postnatal growth patterns in preterm twins and singletons: an etiology-based analysis from the INTERPRACTICE-21st study

Objective Compare birth size and postnatal growth between preterm twins and singletons across gestational age categories and etiologic subgroups. Study design Preterm twins and singletons ( n = 3245) were classified into nine subgroups based on predefined preterm birth etiologies. Postnatal growth (weight, length and head circumference) trajectories were evaluated using multilevel linear regression models accounting for repeated measurements, expressed as z-score changes from birth to hospital discharge based on INTERGROWTH-21 st Standards. Results Twins were significantly smaller at birth than singletons, particularly in late preterm category, but not in the very preterm category. Twin postnatal growth was slower (unadjusted models); most differences attenuated or reversed after adjusting for birth size and key covariates. Twins in the ‘pre-eclampsia’ subgroup showed greater adjusted postnatal weight, whereas weight gain was persistently lower in the ‘perinatal sepsis’ subgroup. Conclusion Preterm twins and singletons have distinct intrauterine and postnatal growth patterns, varying by preterm birth etiology and gestational age categories.