Weight growth velocity of very low birth weight infants: role of gender, gestational age and major morbidities.

It's well known that VLBWI fail to thrive, however it's still unclear how gender, GA and morbidities affect growth pattern: aim of this study is to assess the influence of these factors on weight growth. 262 VLBWI were selected. Weight was recorded daily up to 28 days, weekly up to discharge and during 7 scheduled follow-up visits up to 2 years of corrected age. Individual profiles were fitted with a mathematical function suitable to model selected growth milestones and mean distance and velocity curves were drawn. Effects of gender, GA, major-morbidities, nutritional and respiratory support on individual weight growth milestones were estimated using a multivariate linear model. Each of these variables acts differently on weight growth pattern mainly modifying velocity curves characteristics. In particular, infants with major morbidities weight growth impairment-seen on distance curves at 2 years of corrected age-depends on poor weight velocity during a critical period ending within 4th month of postnatal age, for SGA or BPD infants, starting from 5th month of postnatal for severely neurologically impaired infants. These critical periods could be the most appropriate to identify risk factors for weight growth impairment in VLBWI.

Evaluation of postnatal weight growth in very low birth weight infants.

There is general agreement about the need for longitudinal studies of very low birth weight infants (VLBWI) to evaluate their postnatal growth and to generate distance and velocity charts that allow neonatologists and pediatricians to detect earlier whether a child is not growing adequately. There are no satisfactory growth charts for VLBWI. We analyzed the weight growth of 262 VLBWIs from birth to 2 years of corrected age. Individual growth profiles were fitted with a 7-constant exponential-logistic function suitable for modelling weight growth pattern. After a postnatal weight loss, all VLBWIs showed a late neonatal peak of velocity between the seventh and 21st weeks; the large majority of them also experienced an early neonatal peak between the second and the sixth weeks. Small-for-gestational-age VLBWIs with major morbidities grew less than reference appropriate-for-gestational-age VLBWIs without major morbidities: at 2 years, the difference in weight was about 860 g. The more severe growth impairment in VLBWIs with major morbidities was almost entirely due to the reduced height of the late neonatal peak of velocity. The mathematical function used in this study is expected to be a useful tool to trace model-based longitudinal distance and velocity charts specific for VLBWIs. Moreover, this function also could be used to evaluate to what extent different pathological conditions or nutritional and medical care protocols affect growth kinetics.