Investigating socioeconomic and demographic determinants of suboptimal birth spacing and adverse child growth outcomes in the Indian subcontinent

<p dir="ltr">Background: In Low- and Middle-Income Countries (LMICs) sociodemographic factors influence the timing of births, but it’s unclear if these factors consistently affect the first birth interval (FBI) after marriage and successive birth intervals (SBI). Previously, it has been hypothesized that the chronic effect of socioeconomic stressors can accelerate health deterioration, and explain ethnic disparities, but most research into this “Weathering Hypothesis” (WH) has been conducted in developed countries. This thesis examines, within the Indian subcontinent, how sociodemographic factors affect birth interval length and the relevance of the WH for explaining variation in maternal age-related patterns of child health outcomes.</p><p dir="ltr">Methods: This thesis includes a systematic review to compare factors associated with sub-optimal birth intervals of different parity, and a rapid review to contrast evidence for the Weathering Hypothesis in developed and developing countries. In the first empirical study, we analyzed differences in sociodemographic determinants of FBI and SBI within the 2017-18 Bangladesh Demographic and Health Survey, using recurrent event analysis to account for the dependency between successive births. In the second empirical study, the WH was tested in data from Demographic and Health Surveys for India (2019-2021), Pakistan (2017-2018), and Nepal (2022) by fitting logistic regression models for child health outcomes with interactions between maternal age and ethnicity. Further analysis of intersectionality between maternal age and sociodemographic factors was conducted using pooled DHS data from the Indian subcontinent</p><p dir="ltr">Results: In the systematic review, we found that most studies address FBI and SBI separately. We found that key risk factors such as maternal education and contraceptive use had different associations with FBI and SBI in Bangladesh. The rapid review highlighted a lack of direct application of the WH in the Indian subcontinent and other LMIC countries. When testing the WH, there was some evidence, particularly for stunting, that mothers from socioeconomically disadvantaged backgrounds had an increased risk of adverse child health outcomes during their prime childbearing ages(25-34yrs). However, the health risks associated with marginalized ethnic groups did not generally follow weathering patterns.</p><p dir="ltr">Conclusions: Although there is limited evidence to support classical weathering patterns in the Indian subcontinent, chronic exposure to social inequalities may exacerbate health risks during the prime childbearing years. The identification of demographic and socioeconomic factors influencing birth intervals and child health outcomes may assist the development of targeted interventions for addressing population fertility and reducing inequalities.</p>