Objective Few studies deal with VLBWI postnatal weight growth velocity. An analysis of VLBWI weight growth kinetics up to 2 years is reported and effects on growth of gestational age (GA), weight for GA and bronchopulmonary dysplasia (BPD) are assessed.

Patients and Methods 262 VLBWI were selected, inaccurate GA estimate, major congenital anomalies, necrotizing enterocolitis, death or loss to follow-up within the first year being the exclusion criteria. Weight was recorded daily up to 28 days, weekly up to discharge, then at 1–3–6–9–12–18–24 months of corrected age. Individual growth profiles have been fitted with a 7-constant exponential-logistic function suitable for modelling weight growth pattern. GA, weight for GA and BPD effects were estimated by means of a multivariate linear model.

Results All VLBWI showed a non-linear growth pattern characterised by a late velocity peak between 7th and 21st week, the large majority of VLBWI also experienced an early neonatal peak between 2nd and 6th week. Lower GA delays the age at late peak, but between GA classes differences in weight at 2 years are negligible. BPD and being SGA act reducing late peak’s height during a critical period ending within the 4^th month, so causing a growth impairment still perceivable at 2 years.

Conclusions Our results demonstrate that a single mean value seems to be poor to describe VLBWI growth kinetics. The identified critical period could be the most appropriate to detect growth impairment risk factors in VLBWI and to monitor effects of healthcare and nutritional protocols on growth.