Mediators of socioeconomic inequalities in preterm birth: a systematic review

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.

Changes in preterm and extremely preterm birth rates in Japan after the introduction of obstetrical practice guidelines in 2008

“…The factors affecting preterm births are many, including medical causes. 46,47 In addition, economic and social factors, 48,49 as well as other factors such as anxiety, 50 have been implicated in preterm births. We have not considered these elements and believe that further examinations are necessary in the future.…”

Mediating Factors in the Association of Maternal Educational Level With Pregnancy Outcomes

“…Socioeconomic factors-educational attainment in particular-are associated with adverse pregnancy outcomes. [1][2][3][4][5] However, it is challenging to modify an individual's level of education, and opportunities to seek education are not equally distributed throughout the population. It is therefore of great importance to identify modifiable risk factors through which the association with educational attainment is mediated.…”

“…6 Conventional observational studies have identified some potential mediating pathways, and cardiometabolic risk factors stand out. 1 For instance, prepregnancy body mass index (BMI) and systolic blood pressure (SBP) have been observed to explain most of the association between educational level and gestational hypertension and preeclampsia. 2,3 Smoking has been observed to likely mediate some of the potential association of educational level with preterm birth 7 and low birth weight, 4 but not with the risk of preeclampsia.…”

“…2 For preterm birth, most of the likely association with educational attainment remains unexplained. 1 For yet other pregnancy outcomes, such as ectopic pregnancy, hyperemesis gravidarum, and gestational diabetes, the role of any mediating pathways downstream of educational attainment remains largely unknown. 5,8,9 Thus, there is a need for a systematic evaluation of targetable risk factors that may help reduce socioeconomic inequalities in pregnancy outcomes.…”

Perinatal Health Inequalities in the Industrial Region of Estonia: A Birth Registry-Based Study

“…Systematic reviews have shown significant socioeconomic disparities in ABOs [ 14 , 15 ]. ABOs are also used as one of the health indicators to measure existing health inequalities [ 16 , 17 ].…”