Background and objectives: Data on body mass index (BMI) in infants and toddlers worldwide are lacking, relative to older age groups. This research describes growth (weight, length, and BMI z-score) of New Zealand children under the age of 3 years, and examines differences by sociodemographic characteristics (sex, ethnicity and deprivation).
Methods: Electronic health data were collected by Whānau Āwhina Plunket, who provide free ‘Well Child’ services for approximately 85% of newborn babies in New Zealand. Data from children under the age of 3, who had their weight and length/height measured during 2019, were included in the analysis. The prevalence of high BMI (>95th percentile) was determined, using WHO Child Growth Standards.
Results: Overall, 144,043 observations of child growth between 6 weeks and 27 months of age were included. Between 6 weeks and 27 months of age, the percentage of infants with high BMI (>95th percentile) increased from 2.5% (95% CI: 2.3, 2.7) to 16.4% (95% CI: 15.8, 17.1). The greatest rate of change in prevalence of high BMI occurred between 12 weeks and 6 months of age, with an average increase in prevalence of 0.88% per month. Importantly, the prevalence of infants with a high BMI appears to increase substantially from 6 months of age across sociodemographic indicators examined (sex, ethnicity, deprivation), with a widening prevalence gap by ethnicity occurring from 6 months.
Conclusions: The findings underscore the early onset of BMI disparities by ethnicity and socioeconomic status, highlighting the need for early intervention strategies in infancy to address obesity prevention. Utilising BMI-for-age child growth charts in the ‘Well Child’ setting may aid in early identification and monitoring of adiposity trends in young children, supporting targeted public health efforts.