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Cited by 91Maternal and Neonatal HealthcareInfant Development and Preterm CareHealth disparities and outcomes

The DOI matches its Crossref record; 74 of the 74 references it cites were found in a registry or an index; none of the 226 sources its claims cite is checked for support yet.

Mediators of socioeconomic inequalities in preterm birth: a systematic review

Open access

Abstract

Background: 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. This study therefore aimed to identify mediators of the relationship between maternal SES and preterm birth, assess the strength of evidence, and evaluate the quality of methods used to assess mediation. Methods: Using Scopus, Medline OVID, “Medline In Process & Other Non-Indexed Citation”, PsycINFO, and Social Science Citation Index (via Web of Science), search terms combined variations on mediation, socioeconomic status, and preterm birth. Citation and advanced Google searches supplemented this. Inclusion criteria guided screening and selection of observational studies Jan-2000 to July-2020. The metric extracted was the proportion of socioeconomic inequality in preterm birth explained by each mediator (e.g. ‘proportion eliminated’). Included studies were narratively synthesised. Results: Of 22 studies included, over one-half used cohort design. Most studies had potential measurement bias for mediators, and only two studies fully adjusted for key confounders. Eighteen studies found significant socioeconomic inequalities in preterm birth. Studies assessed six groups of potential 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. There was high confidence of smoking during pregnancy (most frequently examined mediator) and maternal physical health mediating inequalities in preterm birth. Significant residual inequalities frequently remained. Difference-of-coefficients between models was the most common mediation analysis approach, only six studies assessed exposure-mediator interaction, and only two considered causal assumptions. Conclusions: The substantial socioeconomic inequalities in preterm birth are only partly explained by six groups of mediators that have been studied, particularly maternal smoking in pregnancy. There is, however, a large residual direct effect of SES evident in most studies. Despite the mediation analysis approaches used limiting our ability to make causal inference, these findings highlight potential ways of intervening to reduce such inequalities. A focus on modifiable socioeconomic determinants, such as reducing poverty and educational inequality, is probably necessary to address inequalities in preterm birth, alongside action on mediating pathways.

Overview

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TL;DR

This systematic review of 22 observational studies found that socioeconomic inequalities in preterm birth are only partly explained by six groups of mediators, most consistently maternal smoking and maternal physical health. A large residual direct effect of socioeconomic status remained in most studies, and methodological limitations constrain causal inference.

Key findings

  • Of 22 included studies, 18 found significant socioeconomic inequalities in preterm birth; six mediator groups were assessed: maternal smoking, mental health, physical health (including BMI), lifestyle (including alcohol), healthcare, and working/environmental conditions.
  • There was high confidence that smoking during pregnancy mediates inequalities: 16 estimates of proportion eliminated ranged from 2% to 45%, with the largest study (1,390,742 singleton births) reporting 26% for extremely preterm, 33% for very preterm, and 30% for moderately preterm births.
  • There was high confidence for maternal physical health as a mediator, with proportion eliminated ranging from 3% to 22% for physical health measures; evidence for mental health was mixed, and alcohol, working/environmental conditions, and healthcare had low to moderate or inconsistent evidence.
  • Most studies showed a substantial residual direct effect of SES; complete mediation was unlikely by individual variables, though three studies found composites removed statistical significance for SES measures.

Methods

  • Systematic review registered with PROSPERO (CRD42020203613), searching Scopus, Medline OVID, Medline In Process, PsycINFO, and Social Science Citation Index, plus citation and advanced Google searches; inclusion criteria covered observational studies from Jan 2000 to July 2020.
  • After screening, 22 studies were included; data were dual-extracted, quality-assessed using a hybrid approach (risk of bias plus mediation-specific criteria), and narratively synthesised because meta-analysis was not appropriate.
  • The main metric extracted was proportion eliminated; certainty of evidence was assessed considering sample size, quality score, and consistency, with a harvest plot and DAG used to display and integrate findings.

Limitations

  • The review states that different SES measures are potentially not comparable, only eight studies made clear that exposure was measured before outcome, and the search focused on studies explicitly examining mediation, potentially missing extractable mediated effects.
  • The review also states data limitations: some plausible mediators were not examined (e.g., air pollution, urbanicity, domestic violence), mediator measurement was often problematic, preterm birth was mostly treated as homogeneous, and many studies did not estimate confidence intervals or mediator significance.
  • Evident from the text: only two studies fully adjusted for all three key confounders (maternal age, parity, race/ethnicity), only two explicitly considered causal assumptions, and only six assessed exposure-mediator interaction, limiting causal interpretation.

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Integrity signals

Registry

Crossref · 10.1186/s12889-022-13438-9

Cites

74 of 74 references verified0 citation errors · 0 not checkable

Statistics

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Figures

Fig. 1 PRISMA diagram for included studies for the systematic review question
Fig. 1 PRISMA diagram for included studies for the systematic review questionCC BY · PubMed Central
Fig. 2 Harvest plot of proportion eliminated metric for the four most commonly examined mediators. Proportion eliminated: proportion that differences in preterm birth between socioeconomic groups would be reduced by if the mediator was the same for all pregnant women. Colour shows quality score (lighter shade indicates higher score) and shape is significance of indirect effect. Only studies with a significant total effect of SES on preterm birth were included and a study using a continuous measure of smoking was not included. BMI body mass index
Fig. 2 Harvest plot of proportion eliminated metric for the four most commonly examined mediators. Proportion eliminated: proportion that differences in preterm birth between socioeconomic groups would be reduced by if the mediator was the same for all pregnant women. Colour shows quality score (lighter shade indicates higher score) and shape is significance of indirect effect. Only studies with a significant total effect of SES on preterm birth were included and a study using a continuous measure of smoking was not included. BMI body mass indexCC BY · PubMed Central
Fig. 3 Causal pathway based on results of the studies included in the systematic review
Fig. 3 Causal pathway based on results of the studies included in the systematic reviewCC BY · PubMed Central

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Citations

Cites

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Research works printed but not linked: 2

  1. Thomas J, Brunton J, Graziosi S. EPPI-Reviewer 4: software for research synthesis, EPPI-Centre Software. London: Social Science Research Unit, UCL Institute of Education; 2010.
  2. Dooley P. Examining individual and neighborhood-level risk factors for delivering a preterm infant. Doctor of Philosophy (PhD) thesis. Cincinnati: University of Cincinnati; 2009:189.

Cited by

Metadata

Authors
McHale, P., Maudsley, G., Pennington, A., Schlüter, D. K., Barr, B., Paranjothy, S., & Taylor-Robinson, D.
Affiliations
  • University of Liverpool (GB)
  • University of Aberdeen (GB)
Corresponding author
McHale, Philip
Venue
BMC Public Health
Published
2022-06-07
Volume
22
Issue
1
Pages
1134-1134
ISSN
1471-2458 (ISSN-L)
OpenAlex
W4281739443
Cited by
89
References
74
Citations by year
2026: 27 · 2025: 21 · 2024: 21 · 2023: 16 · 2022: 3
FWCI
3.46
Type
journal article
Language
en
Open access
Locations
  • BMC Public Health (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • PubMed Central (publishedVersion, cc-by)
  • Aberdeen University Research Archive (Aberdeen University) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • National Institute for Health and Care Research
  • Medical Research Council (MR/P008577/1, MR/T00794X/1)
Topics
  • Health Sciences › Medicine › Pediatrics, Perinatology and Child Health › Maternal and Neonatal Healthcare
  • Health Sciences › Medicine › Pediatrics, Perinatology and Child Health › Infant Development and Preterm Care
  • Social Sciences › Health › Health disparities and outcomes
Keywords
preterm birth, socioeconomic disparities, maternal socioeconomic status, mediation analysis, maternal smoking, maternal mental health, maternal physical health, body mass index, alcohol consumption, health care access, working conditions, environmental factors, poverty, educational inequality
MeSH terms
Female, Humans, Infant, Newborn, Pregnancy, Social Class, Socioeconomic Factors, Cohort Studies, Body Mass Index, Premature Birth

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Semantic Scholar’s data is described in: Kinney, R., et al. (2023). The Semantic Scholar Open Data Platform. arXiv:2301.10140.