Obstetric Comorbidity Scores and Disparities in Severe Maternal Morbidity Across Marginalized Groups

BACKGROUND
A recently developed obstetrical comorbidity scoring system enables the comparison of severe maternal morbidity rates independent of health status at the time of birth hospitalization. However, the scoring system has not been evaluated in racial-ethnic and socioeconomic groups or used to assess disparities in severe maternal morbidity.
OBJECTIVE
This study aimed to evaluate the performance of an obstetrical comorbidity scoring system when applied across racial-ethnic and socioeconomic groups and to determine the effect of comorbidity score risk adjustment on disparities in severe maternal morbidity.
STUDY DESIGN
We analyzed a population-based cohort of live births that occurred in California during 2011 through 2017 with linked birth certificates and birth hospitalization discharge data (n=3,308,554). We updated a previously developed comorbidity scoring system to include the International Classification of Diseases, Ninth and Tenth Revisions, Clinical Modifications diagnosis codes and applied the scoring system to subpopulations (groups) defined by race-ethnicity, nativity, payment method, and educational attainment. We then calculated the risk-adjusted rates of severe maternal morbidity (including and excluding blood transfusion–only cases) for each group and estimated the disparities for these outcomes before and after adjustment for the comorbidity score using logistic regression.
RESULTS
The obstetric comorbidity scores performed consistently across groups (C-statistics ranged from 0.68 to 0.76; calibration curves demonstrated overall excellent prediction of absolute risk). All non-White groups had significantly elevated rates of severe maternal morbidity before and after risk adjustment for comorbidities when compared with the White group (1.3% before, 1.3% after) (American Indian-Alaska Native: 2.1% before, 1.8% after; Asian: 1.5% before, 1.7% after; Black: 2.5% before, 2.0% after; Latinx: 1.6% before, 1.7% after; Pacific Islander: 2.2% before, 1.9% after; and multi-race groups: 1.7% before, 1.6% after). Risk adjustment also modestly increased disparities for the foreign-born group and government insurance groups. Higher educational attainment was associated with decreased severe maternal morbidity rates, which was largely unaffected by comorbidity risk adjustment. The pattern of results was the same whether or not transfusion-only cases were included as severe maternal morbidity.
CONCLUSION
These results support the use of an updated comorbidity scoring system to assess disparities in severe maternal morbidity. Disparities in severe maternal morbidity decreased in magnitude for some racial-ethnic and socioeconomic groups and increased in magnitude for other groups after adjustment for the comorbidity score.