Presented at the Neonatal Society 2009 Spring Meeting.
Gutierrez A1, Borja MC2, Modi N3, Cole TJ4
1,3 Section of Neonatal Medicine, Imperial College London, Chelsea & Westminster Campus, SW10 9NH, UK
2,4 UCL Institute of Child Health, 30 Guilford Street WC1N 1EH, UK
Background: The utility of weight growth velocity (GV) is founded on the concept that growth assessment best defines overall health and predicts performance and survival. However, the calculation of GV (g/kg/day) is labour intensive and investigators have estimated GV with varying approaches, making comparisons across studies difficult. No uniform method for calculating growth velocity among extremely preterm infants has been agreed and several methods have been described and are of varying degrees of complexity.
Objective: To compare the agreement between two mathematical models for calculating weight growth velocity in a contemporary cohort of extremely preterm infants:
where BW is birth weight and W is weight in grams, T is age in days, 1 and 2 indicate the two measurement occasions and ln is the natural logarithm (1).
Methods: Infants born ≤ 34 weeks gestation admitted between August 2007 and August 2008 to the Chelsea & Westminster neonatal unit were included. Weight growth velocity (g/kg/day) was calculated from admission up to discharge on a weekly basis. The Bland-Altman plot was used to assess the level of agreement between the two models (2).
Results: 171 preterm infants, with mean (SD) gestational age 30.1 (3.3) weeks and BW 1413 (534) g respectively, were included. Mean growth velocity was 3.7 (6.2) g/kg/day with model [a] and 3.8 (5.9) g/kg/day with model [b]. The 95% limits of agreement were 3.3 to +3.3 g/kg/day.
Conclusion: Postnatal growth in extremely preterm infants calculated with the two models showed good agreement on the whole, though in a minority of cases the discrepancy exceeded 4 g/kg/day. For day to day use the simpler 2-point model [a] is recommended.
References
1. Patel AL., Engstrom JL, Meier PP, Kimura RE. Accuracy of Methods for Calculating Postnatal Growth Velocity for Extremely Low Birth Weight Infants. Pediatrics 2005; 116:1466-1473.
2. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;8:307-10.