Changes in objectively measured BMI in children aged 4-11 years: data from the National Child Measurement Programme.

Background: This study looked at the degree of weight gain between the first (Reception) and last year (Year 6) of primary school and how weight status in Reception predicts becoming overweight/obese by Year 6.

Methods: A longitudinal sample of 1863 children was created using two time points (2006/7, 2012/13) from the National Child Measurement Programme (NCMP) in South Gloucestershire. T-test and logistic regression were used to test the difference between the BMI z-scores and BMI percentiles, and predict the probability of being overweight (BMI ≥ 85th) or obese (≥95th) at Year 6 based on BMI percentile in Reception.

Results: Of those children who were obese at Reception age, 68% were obese at Year 6. Compared with children with a BMI in the 2nd to 49th percentile range, children between the 75th and 84th percentiles of BMI at Reception age were 10 times more likely (odds ratio (OR) = 10.18, P < 0.01), and those with a BMI between the 85th and 94th percentiles were 13 times more likely (OR = 13.38, P < 0.01), to become obese by Year 6. Boys were more likely than girls to revert to a healthy weight.

Conclusions: This is the first study to link data from the NCMP. It provides estimates of prevalence and offers new evidence on obesity emergence and gender differences.