Infant Body Mass Index vs. Weight-for-Lenght: Time To Revisit The Guidelines?

​
​Izzuddin Aris, PhD

Children’s physical growth has long been recognized as an indicator of health and wellness. Infancy, a time where substantial growth occurs, is identified as an important period for the development of future disease risk – many studies have shown that excessive weight gain during infancy is associated with an increased risk for subsequent childhood obesity and development of cardiometabolic diseases. Traditionally, infant growth (< 2 years of age) is assessed through weight-for-length, the predominant standard used internationally and currently recommended by the American Academy of Pediatrics and Center for Disease Control and Prevention (CDC). Weight-for-length growth charts however, don’t account for age which means that shorter (but older and therefore heavier) infants could be compared with younger infants of the same length with respect to weight, and with older infants labelled “heavier”, an effect primarily due to age.

In 2006, the World Health Organization (WHO) provided age- and sex-specific body mass index (BMI – calculated as weight in kilograms divided by height in meters squared) charts that describes the pattern of BMI growth for children ages 0 to 5 years, which overcomes this weight-for-length limitation. Because the CDC and WHO charts are available, practitioners and researchers now can choose which growth charts to use. Therefore, it’s important to understand how each growth charts estimate later clinical outcomes, because practitioners may predict differing later health outcomes depending on which anthropometric measure they use..
In our latest study, we used data from two longitudinal cohorts in the United States (Project Viva) and Belarus (Promotion of Breastfeeding Intervention Trial [PROBIT]) to assess the relationships of being overweight by the CDC and WHO growth charts during the first 2 years of life with various cardiometabolic outcomes during early adolescence. By analyzing the data in two very different populations, we were able to better assess the generalizability of our findings. We found that children who were categorized as ever overweight (vs. children who were never overweight) during 6‒24 months of age were more likely to have an adverse cardio-metabolic profile (i.e., higher fat mass index, insulin resistance and metabolic risk score) in early adolescence, yet these relationships did not differ greatly when weight-for-length or body mass index was used to define overweight in either cohort. Neither growth chart or metric outperformed each other in predicting these cardiometabolic outcomes.

These observations suggest that choice of using weight-for-length or body mass index in children below 2 years does not greatly affect the ability to predict future adiposity and cardio-metabolic outcomes. More specifically, if pediatricians were to switch from using the CDC weight-for-length charts to WHO body mass index charts when defining overweight in children younger than 2 years of age, the ability to estimate future cardiometabolic outcomes would not be significantly affected. Existing guidelines by the CDC already suggest the use of body mass index for growth and obesity screening in children older than 2 years. Applying the same metric for children below 2 years would therefore streamline clinical practice. Thus, if body mass index replaced weight-for-length for assessment of weight status in children below 2 years, it could improve monitoring of longitudinal growth patterns from infancy to adulthood without the need to transition between differing growth metrics after 2 years. We acknowledge that these findings would benefit from replication in other population cohorts; nevertheless, they have implications for practitioners on using body mass index to monitor the weight status of children younger than 2 years.

Study was also featured in: https://www.medpagetoday.com/pediatrics/generalpediatrics/75247