Background Neonatal and infant mortality rates in England and Wales have declined in recent years. However, disparities in outcomes persist. This study aimed to describe the variation in risks of adverse birth outcomes across ethnic groups and socioeconomic circumstances, and to explore the evidence of mediation by socioeconomic circumstances on the effect of ethnicity on birth outcomes.

Methods The data came from the 4.6 million singleton live births in England and Wales between 2006 and 2012. Socioeconomic circumstances was measured using the Index of Multiple Deprivation (IMD). We estimated the slope and relative indices of inequality to describe differences in birth outcomes across IMD, and the proportion of the variance in birth outcomes across ethnic groups attributable to IMD. We investigated mediation by IMD on birth outcomes across ethnic groups using structural equation modelling.

Results Neonatal mortality, infant mortality and preterm birth risks were 0.2%, 0.3% and 5.6% respectively. Babies in the most deprived areas had 47% to 129% greater risk of adverse birth outcomes than those in the least deprived areas. Minority ethnic babies had 48% to 138% greater risk of adverse birth outcomes compared with white British babies. Up to a third of the variance in birth outcomes across ethnic groups was attributable to differences in IMD, and there was strong statistical evidence of an indirect effect through IMD in the effect of ethnicity on birth outcomes.

Conclusion There is evidence that socioeconomic circumstances could be contributing to the differences in birth outcomes across ethnic groups.