Assessing the impact of adjusting for maturity in weight status classification in a cross-sectional sample of UK children

Objectives
To compare the weight categorisation of a cohort of UK children using standard procedures (i.e., comparing BMI centiles to age-matched UK reference data) versus an approach adjusted for maturation status (i.e., matching relative to biological age). 
Design Analysis of data collected from an observational study of UK primary school children. Setting Schools in south west England.Participants Four hundred and seven 9-11 year old children (98% white British)
Main outcome measures: Weight status was classified using BMI centiles using (i) sex and chronological-age matched referents, and (ii) sex and biological-age matched referents (based on % of predicted adult stature) relative to UK 1990 reference growth charts. For both approaches, children were classified as a normal weight if >2nd centile and <85th centile, overweight if 85th and <95th centiles, and obese if ≥95th centile. Results Fifty-one children (12.5%) were overweight, and a further 51 obese (12.5%) according to standard chronological-age matched classifications. Adjustment for maturity resulted in 32% of overweight girls, and 15% of overweight boys being reclassified as a normal weight, and 11% and 8% of obese girls and boys respectively being reclassified as overweight. Early maturing children were 4.9 times more likely to be reclassified from overweight to normal weight than ‘on-time’ maturers (odds ratio 95% CI=1.3 to 19).
Conclusions: Incorporating assessments of maturational status into weight classification resulted in significant changes to the classification of early-maturing adolescents. Further research exploring the implications for objective health risk and wellbeing is needed.