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Growth assessment of preterm infants using detailed anthropometry

Presented at the Neonatal Society 2016 Spring Meeting.

Ashton JJ, Johnson M, Pond J, Crowley P, Dimitrov B, Pearson F, Beattie RM

University Hospital Southampton/University of Southampton

Background: Preterm infants display slower ex-utero growth and altered body composition (lower fat-free mass, higher percentage body fat) compared to term counterparts; rendering them at risk of morbidity and mortality. Weight is known to fluctuate and does not represent accrual of lean mass or changes in body composition. In children mid-upper arm circumference (MUAC) is a validated measure of nutritional status (lean mass). This study aimed to investigate the utility of determination of growth using MUAC and mid-thigh circumference (MTC) in infants born below 30 weeks gestation.

Methods: Infants were recruited within 1 week of admission to the neonatal unit in Southampton. MUAC and MTC were measured in these infants at recruitment and at weekly intervals until discharge; each measurement was performed in triplicate on individual blank tapes to avoid bias (a mean value was calculated). All limbs were measured each week by the same 3 people. In addition weekly measurements of weight, length and head circumference were collected. Data were analysed by corrected gestational age; infants were added into the analysis at the week they were born and remained in the analysis (e.g. 23 week infants added 23 weeks CGA and included in 24 weeks CGA data when 1 week old etc.) and by unadjusted age (week of life). This study is funded by the Biomedical Research Centre for Nutrition (Southampton) and has full ethical approval (REC 14/SC/1275).

Results: 46 infants were recruited. Median duration of measurement was 7.5 weeks (1-19 weeks). Median gestational age at birth was 26 weeks (23-29 weeks). Analysis of unadjusted data by curve estimation displayed a mean increase of 3.94mm/week for left MUAC (p=<0.0001), 3.92mm/week for right MUAC (p=<0.0001), 6.1mm/week for left MTC (p=<0.0001) and 6.3mm/week for right MTC (p=<0.0001). A significant change was also seen in MUAC and MTC when measured at weekly intervals using CGA data.

Growth assessment of preterm infants using detailed anthropometry

Unadjusted data were used to calculate coefficients of determination (R2) using a growth regression model for individual measures; left MUAC 0.992, right MUAC 0.989, left MTC 0.989 and right MTC 0.995. All 4 measures fitted a growth model as closely as weight (0.995), length (0.985) and head circumference (0.989). There was high concordance between left and right MUAC/MTC; comparing unadjusted age data; mean left MUAC and right MUAC generated a correlation coefficient of 0.999 (Pearson) (p=<0.0001); left MTC and right MTC generated a correlation coefficient of 0.998 (Pearson) (p=<0.0001). Correlation of mean weight and length with additional mean anthropometric measures demonstrated concordance for all measures.

Conclusion: These data demonstrate the potential utility of MUAC and MTC as a measure of growth in preterm infants and were accurately reproducible over time. These preliminary data show statistically significant correlation between standard anthropometric measures and MUAC/MTC. Further study of more infants, combined with nutrient intake data, is vital to confirming MUAC/MTC as a useful and minimally invasive measure of growth and body composition in preterm infants.

Corresponding author: j.ashton@soton.ac.uk

Acknowledgement: JJA is supported by a NIHR academic clinical fellowship (Paediatrics).

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