Background: Early adiposity rebound (AR), defined as the age at which body mass index (BMI) reaches its nadir before increasing, is a strong predictor of later obesity and cardiometabolic risk. Socioeconomic status is inversely associated with childhood obesity; however, evidence linking resource-based socioeconomic indicators, such as household income, to AR timing is inconsistent. Prior studies have largely relied on conventional regression approaches that may inadequately address confounding.

Methods: We analyzed data from 927 participants in a U.S. longitudinal birth cohort with repeated BMI measures from birth to age 15 years. AR age was estimated using sex-specific mixed-effects cubic models of log-transformed BMI, with AR defined as the minimum predicted BMI between ages 2 and 9 years. Early AR was defined as <5 years. The exposure was early childhood household income, operationalized as an income-to-need ratio <1.85 versus ≥1.85 averaged across ages 1–24 months. Propensity scores were estimated using early-life sociodemographic and parental factors measured before age 2 years. After trimming and 1:2 nearest-neighbor matching within multiply imputed datasets, modified Poisson regression estimated risk ratios (RR) for early AR.

Results: Among 818 children with valid AR estimates, 49.5% experienced early AR. Propensity score matching achieved acceptable covariate balance (all standardized mean differences <0.2). Low household income was not associated with early AR (RR=0.91; 95% CI: 0.71–1.17). Findings were consistent in regression-adjusted and complete-case analyses.

Conclusions: Conclusions: In high-income countries such as the United States, children from low socioeconomic households are disproportionately affected by obesity and related risk factors, and early adiposity rebound is often presumed to follow this gradient. In this quasi-causal analysis, early childhood household income was not associated with AR timing. These findings suggest that extrapolating broader socioeconomic disparities to all developmental markers may obscure distinct etiologic pathways and underscore the need to identify specific mechanisms driving early adiposity rebound.