title: Understanding the effects of socioeconomic inequalities on preterm birth: epidemiological studies into differential exposure, differential susceptibility and differential consequences
Creators: name: McHale, Philip
Publisher: name: University of Liverpool Repository
Year: 2024

description: Introduction
Rates of preterm birth are substantial with significant inequalities. Understanding the role of risk factors on the pathway from maternal socioeconomic status (SES) to preterm birth can help inform interventions and policy. Additionally, Children who are born pre-term have an increased risk of negative health and education outcomes. These outcomes are socially patterned but it is not clear how the effects of preterm birth are modified by socioeconomic circumstances. My hypotheses are that inequalities in gestational age at birth can be explained by different prevalence of risk factors across socioeconomic strata, and that the consequences of preterm birth are modified by SES.
Methods
My thesis is split into two broad areas; mediation and interaction. The mediation aspect of my analysis first consists of a systematic review, then utilising two data sources to estimate two measures of mediation. (1) The proportion eliminated is the percentage of the effect of SES on low gestational age at birth that would be eliminated by removing the mediators. (2) The proportion mediated is the percentage of the effect removed by equalising the distribution of the mediators across socioeconomic groups. Local hospital data from Liverpool Women’s Hospital was used to estimate the mediated effects of maternal smoking during pregnancy and pre-pregnancy BMI. Data from Wales from the SAIL databank was used to estimate the mediated effects of maternal smoking during pregnancy, maternal mental health, maternal physical health and obstetric conditions during pregnancy. The interaction aspect of my analysis consists of a systematic review looking at interaction and effect modification of preterm birth consequences by socioeconomic status on health and educational outcomes.
Results
Existing evidence show socioeconomic inequalities in preterm birth are partly explained by six groups of mediators: maternal smoking; maternal mental health; maternal physical health (including body mass index (BMI)); maternal lifestyle (including alcohol consumption); healthcare; and working and environmental conditions. My analyses show
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maternal smoking during pregnancy is a significant mediator of preterm birth inequalities; maternal mental and physical health (including BMI) during pregnancy, and obstetric conditions mediate to a lesser extent. My systematic review of interaction suggests that the consequences of preterm birth on cognitive and mental health outcomes is exacerbated by low SES, and vice versa (the impact of low SES is exacerbated by preterm birth).
Conclusion
My thesis uses systematic review approaches, and counterfactual causal mediation analysis to explore how life-course socioeconomic inequalities are generated in relation to preterm birth. I identify several potential variables that explain inequalities in the rate of preterm birth, including maternal smoking in pregnancy, maternal physical and mental health and environment. However, my empirical analyses find smoking is the main mediator, and residual inequalities remain after the effect of mediators is removed. Finally, I identify that the negative consequences of preterm birth on mental health and cognitive ability are exacerbated by exposure to low socioeconomic circumstances.