PURPOSE: To measure associations of area-level racial and economic residential segregation with severe maternal morbidity (SMM).

METHODS: We conducted a retrospective cohort study of births at two Philadelphia hospitals between 2018-2020 to analyze associations of segregation, quantified using the Index of Concentration at the Extremes (ICE), with SMM. We used stratified multivariable, multilevel, logistic regression models to determine whether associations of ICE with SMM varied by self-identified race or hospital catchment.

RESULTS: Of the 25,979 patients (44.1% Black, 35.8% White), 1,381 (5.3%) had SMM (Black [6.1%], White [4.4%]). SMM was higher among patients residing outside (6.3%), then inside, (5.0%) Philadelphia (P<0.001). Overall, ICE was not associated with SMM. However, ICE (higher proportion of White vs. Black households) was associated with lower odds of SMM among patients residing inside Philadelphia (aOR 0.87, 95% CI: 0.80-0.94) and higher odds outside Philadelphia (aOR 1.12, 95% CI: 0.95-1.31). Moran's I indicated spatial autocorrelation of SMM overall (P<0.001); when stratified, autocorrelation was only evident outside Philadelphia.

CONCLUSIONS: Overall, ICE was not associated with SMM. However, higher ICE was associated with lower odds of SMM among Philadelphia residents. Findings highlight the importance of hospital catchment area and referral patterns in spatial analyses of hospital datasets.