Adjusting for maturity
We have developed a spreadsheet to calculate maturity adjusted BMI percentiles for any child for whom you know their height and weight, plus the heights of both (biological) parents. It’s a non-invasive, reliable method of assessing a child’s stage of development that allows you to consider their weight relative to others of their biological age, in addition to those of the same chronological age. The spreadsheet calculates a child’s level of maturity (i.e., if they are early, on-time, or late – and by how much) from the % of their expected adult height they have so far achieved, vs what is usual for children their age (relative to UK 1990 growth charts). It provides an adjusted BMI percentile which you can compare with the standard percentile (i.e., for children of their age in months), to take into account when advising parents whether or not their child’s weight is of concern.
This screenshot shows how the calculator works (along with these instructions!). You just enter the values you have in the pale green boxes on the left, click on submit, and the results are generated on the right. You can see the BMI of the child, the percentile of this BMI relative to other children of their age, and an adjusted BMI for their level of maturity. In this example, the top row of boxes on the right indicates that this boy is a slightly early maturer, and as such adjusting for maturity there is a slight change to his BMI percentile. But according to both the standard and adjusted measure, he is a healthy weight for his age.
When we adjusted for maturity for a cohort of 450 UK Year 6 children (age 10-11), we found that early maturing children were far more likely to be classified as overweight or obese than their on-time or late maturing peers; 32% of overweight girls and 15% of overweight boys would have been considered a healthy weight using maturity adjusted BMI percentiles, and 11% and 8% of obese girls and boys respectively being reclassified as overweight.
This reclassification system is already used in sporting organisations – to adjust competition to children of more equal stages of physical development, and ensure late-maturing children are not overlooked. In the health setting, it may help us to consider whether the greater BMIs of early maturing children are a real indication of health risk, or just a function of their advanced stage of pubertal development.
Unfortunately the calculator to adjust BMI percentiles for maturity status is on excel, which is not supported by this website – we’re working on solving this, but we’d be happy to send it to you by email if you send through a request on the form below: