Abstract
OBJECTIVE: To evaluate change in the incidence of failure to thrive (FTT) based on selected growth percentile criteria and diagnostic codes before and after a switch in growth curves. METHODS: We performed a retrospective cohort study of children 2 to 24 months of age in a large primary care network that switched its default growth curve from the Centers for Disease Control and Prevention (CDC) reference to the World Health Organization (WHO) standards in 2012. We compared the incidence of FTT defined by growth percentile criteria (using the default growth curve at the time of each measurement) and by International Classification of Diseases, Ninth Revision, codes in the 3 years before and after the CDC-WHO switch using an interrupted time series analysis. We performed these analyses stratified by age group (≤6 months and >6-24 months). RESULTS: We evaluated 83,299 children. Among those ≤6 months, increases in FTT incidence were found in both growth-percentile and clinician-diagnosis criteria at the CDC-WHO switch (P < .05). Among those >6 to 24 months, decreases in FTT incidence were found by growth-percentile criteria at the CDC-WHO switch (P < .05), but no significant changes were found in FTT incidence by diagnostic codes. CONCLUSIONS: When switching from the CDC to the WHO growth curves, changes in the incidence of FTT by growth-percentile and clinician-diagnosis criteria differed for younger versus older infants. Factors beyond growth likely influence the decision to diagnose a child as having FTT and may differ in younger compared to older infants.