Introduction This study analyses the DHS 1993, 2000 and 2006-07 and NFSS 2009 survey data to investigate trends, inequalities and determinants of low birth weight (LBW) in Sri Lanka.

Methods We re-evaluated recent trends in LBW incidence, adjusting for changes in the coverage of DHS surveys to ensure comparability, and used multivariate logistic regression to investigate determinants. We quantified the degree of economic inequality using wealth and concentration indices, and assessed the contribution of determinants to inequality by decomposition.

Results There was a continuing, but slowing decline in LBW incidence, reaching 17% during 2001/02-2006/07, whilst very low birth weight incidence declined from 0.9% to 0.6%. Concentration indices reveal persistent, large economic inequalities in LBW incidence. Maternal body mass index (BMI), height and education, altitude and Indian Tamil ethnicity were the major determinants of LBW, with supply of ‘Thriposha’ having no significant impact. Accounting for maternal BMI and height largely eliminates the impact of economic status, and reduces the impact of ethnicity. Decomposition analysis reveals the major contributors to the inequalities are maternal BMI (21%), height (12%) and education (14%), ethnicity (9%) and altitude (7%).

Conclusions The results imply that food insecurity mediates the association of LBW with poverty, and is the major amenable risk factor. The impact of maternal height and Indian Tamil ethnicity suggests that epigenetic mechanisms play a role, and that reductions in LBW incidence will take considerable time. There is a need to substantially improve the effectiveness of interventions to reduce LBW in coming generations