Introduction
In 2021, globally, cardiometabolic diseases (CMDs) accounted for 35% of the 1.73 billion disability-adjusted life years (DALYs) attributed to non-communicable diseases. The Healthy Life Trajectories Initiative (HeLTI), a four-country randomised controlled trial based on the developmental origins of health and disease(DOHaD) concept, evaluates whether integrated longitudinal public health interventions started prepregnancy reduce the risk of childhood adiposity and, consequently, the development of CMDs in the offspring. This paper presents the protocol for the economic evaluation of the interventions in the Indian arm of HeLTI. The aim is to facilitate the translation of effective and affordable preventive strategies that mitigate the health, social and economic burden of CMDs.

Methods and analysis
A within-trial economic evaluation will be conducted from provider, health system and societal perspectives. Costs will be identified using the activity-based costing method mapped onto a theory-of-change framework that attributes interventions to health outcomes. Costs will include both direct and indirect costs as well as capital and recurring costs. Cost data will be collected using project accounts, time-use tools, surveys and key informant interviews. The incremental cost-effectiveness ratio (ICER) will be estimated for the fat mass index, a measure of adiposity, the primary health outcome, at the fifth year of offspring. Cost-utility and cost-consequence results will be presented for health-related quality of life (HRQoL) and other secondary health outcomes, respectively, in mothers and offsprings. Sensitivity of the results to assumptions will be analysed and uncertainty intervals will be presented. Equity impact of the outcomes will be assessed using the social determinants of health framework.

Ethics and dissemination
The study has been approved by the ethics committees of the lead local institutions, CSI Holdsworth Memorial Hospital (Ref CSIHMH/ERU2019/1) and Swami Vivekananda Youth Movement (Ref IRB 004/2020-21). Findings will be disseminated through scholarly articles, policy briefs, opinion pieces, conferences, interactive sessions with stakeholders and the HeLTI website.

Trial registration number
ISRCTN20161479