Background Preterm birth is a major public health problem, affecting 8% of births in the UK overall with significant socioeconomic inequalities observed. 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 (SEC).

Methods Systematic review of quantitative observational studies of an interaction, or effect modification, between preterm birth and SEC. Searches were conducted from five databases between January 2000 and June 2020, and all were identified for dual screening based on title and abstract review. Inclusion criteria was comparison across SEC and gestational age, interaction between the two, or stratification by either, and health or education as outcome. All included studies were citation searched. All studies were narratively synthesised and quality assessed.

Results After searches, 52 studies were identified for full text screening, of which nine met inclusion criteria. Citation searching produced ten more studies. The final sample (19) covered eight countries (all North America and Europe). Forty outcomes were identified, split into four categories; pre-school, primary school (5–11), secondary school (11–18), and post-school (18–29). Outcomes for pre-school was development/cognitive, school was cognitive/performance, and post-school was socioeconomic status. Health outcomes were neonatal mortality, ADHD medication prescription, and psychiatric diagnosis or disability post school. Varied measures of socioeconomic status were used as exposure. The majority (16) categorised preterm birth. Of the 18 studies that examined interaction, seven studies found there was a statistically significant interaction between measure of SEC and preterm birth. All interactions found demonstrate that the negative influence of preterm birth was stronger for those in low SEC. Outcomes which provide significant interaction included; cognitive outcome at 18, prescription of ADHD medication in childhood and adolescence, educational attainment at all levels, and psychiatric admissions in 23 to 29.

Discussion There is some evidence of an interaction between preterm birth and SEC on outcomes for children and young people; the negative effects of preterm birth were exacerbated by low SEC. The remaining evidence suggests the effects accumulate; this is potentially due to underpowered studies. A limitation of the evidence is reporting, some studies only reported whether interaction was significant. This evidence has important policy implications; the potential exacerbation, added to the socioeconomic inequalities in preterm birth, means there is a cohort of children with increased vulnerability, with specific needs that require further investigation.