Population-level obesity surveillance: monitoring childhood body mass index z-score in a safety-net system.

OBJECTIVE: To determine the utility of repeated patient-level body mass index (BMI) measurements among higher-risk patients seen at safety-net clinics as a community-level monitoring tool for overweight and obesity population trends. METHODS: Data from a network of urban, federally qualified community health centers with computerized tracking of BMI at sequential outpatient visits were analyzed. We performed a longitudinal observational study over 8 years (2005-2012) with children stratified by weight status groups on the basis of BMI. Changes in BMI z-scores were used to estimate population trends among children 2 to 11 years old, with at least 2 visits (at least 1 year apart), for whom weight and height were measured. RESULTS: Among children (n = 33,542), the rate of overweight was 16% and rate of obesity was 18% at their last visit. Children were followed for an average of 3.24 ± 1.76 years to measure trends and change in weight status from earlier to later childhood. Children who were obese at first visit had increased odds (adjusted odds ratio 27.8, 95% confidence interval 25.6-30.2) of being obese by last visit. Mean change in BMI z-score per person-year of observation was 0.10 ± 0.38, with a differing rate of change based on weight status category at last visit (not overweight = 0.06 ± 0.39; overweight = 0.17 ± 0.34; obese = 0.19 ± 0.36). Change in BMI z-score per person-year decreased for 40% of obese children; however, their weight status group remained unchanged. CONCLUSIONS: Childhood obesity prevalence was high, with substantial progression to overweight and obesity from first to last visit. Clinically derived BMI z-score per person-year measures can effectively show population trends not observed using standard weight status categories.

What can providers learn from childhood body mass index trajectories: a study of a large, safety-net clinical population.

OBJECTIVE: To describe childhood weight gain using body mass index (BMI) z-score trajectories in a low-income urban safety-net population and identify among gender- and race/ethnicity-specific groups any trends for increased risk. METHODS: A retrospective cohort study was conducted among 2- to 12-year-old patients (2006-2013) visiting a safety-net provider. BMI z-score trajectories were calculated overall, for gender- and race/ethnicity-specific groups, and for peak BMI percentile subgroups to describe weight gain longitudinally. RESULTS: From 2006 to 2013, a total of 26,234 eligible children were followed for an average of 3.7 years. At baseline (mean age, 4.2 years), 74% of patients were at a normal weight compared to 65% at most recent observation (mean age, 7.8 years). All gender and race/ethnicity subgroups showed increasing average BMI z-scores during childhood. Children consistently under the 50th percentile and those of white race had the most stable BMI z-score trajectories. BMI z-score increased with increasing age in all subgroups. Hispanic boys and black girls had the most significant increase in BMI z-score during this observation period. Children observed in early childhood and whose BMI exceeded the 95th percentile at any time were often already overweight (20%) or obese (36%) by 3 years of age. CONCLUSIONS: The entire population demonstrated an upward trend in BMI z-score trajectory. This trend was most notable among black girls and Hispanic boys. Many obese children were already overweight by age 3, and persistence of obesity after 3 years of age was high, suggesting that intervention before age 3 may be essential to curbing unhealthy weight trajectories.