Does Low birth weight exacerbate socioeconomic inequalities in child undernutrition in Sri Lanka?

We analysed the 2016 Demographic and Health Survey to investigate the effect of low birth weight (LBW) and socioeconomic inequalities in child undernutrition outcomes in Sri Lanka. Anthropometric data from 7,259 children aged 6–59 months were examined, using underweight, stunting, and wasting as outcomes and LBW as the primary predictor. We applied three-level random intercept logistic regression and estimated socioeconomic inequality measures. Our sample included 16.9% LBW children, with 20.7% underweight, 18.2% stunted, and 14.5% wasted. LBW children had significantly increased odds of being stunted [AOR (95% CI) = 3.00 (2.39, 3.78)], wasting [AOR (95% CI) = 2.23 (1.78, 2.74)] and underweight [AOR (95% CI) = 2.95 (2.45, 3.52)]. LBW children in poor households, born to Indian Tamil mothers, faced greater stunting risks [AOR (95% CI) = 1.74 (1.11, 2.72)]. Significant heterogeneity was observed between households within communities. LBW significantly increases undernutrition among children under five, underscoring the need for targeted, multi-sectoral interventions to address child malnutrition in Sri Lanka.