Ethnic Disparities in Severe Maternal Morbidity and the Contribution of Deprivation: A Population-Based Causal Analysis.

Objective: To investigate the association between ethnicity and severe maternal morbidity (SMM) in England and the mediating effects of neighbourhood-level socio-economic deprivation across detailed ethnic groups.

Design: Population-based nationwide cohort study using English Hospital Episode Statistics Admitted Patient Care (HES APC) data.

Setting: All hospital births in NHS facilities in England between 1 January 2013 and 31 March 2023.

Population: A cohort of 3 839 156 women aged 10- 55 years with births of ≥ 20 weeks' gestation.

Methods: Multivariable fixed and mixed-effects Poisson regression models were used to estimate adjusted risk ratios (RR) for SMM across 10 ethnic groups compared to White women and for each ethnic group in different deprivation quintiles compared to White women in the least deprived neighbourhoods, respectively. Causal mediation analysis was used to calculate the proportion of the association mediated by deprivation.

Main outcome measures: The modified English Maternal Morbidity Outcome Indicator (EMMOI), a composite outcome of SMM.

Results: Minoritised ethnic groups experienced higher SMM risks than White women, with the highest risk for Black African women (RR 1.96, 95% CI: 1.82-2.02) and Bangladeshi women (RR 1.97, 95% CI: 1.88-2.07) compared to White women. The strength of the association varied across ethnic subgroups. Most of the effect of ethnicity on SMM was not mediated by deprivation (11%-29%).

Conclusions: Deprivation plays a minor role in ethnic disparities in SMM. Policies must address the unique challenges faced by minoritised ethnic women.