Racial and Ethnic Disparities in Anemia and Severe Maternal Morbidity

To evaluate antepartum anemia prevalence by race and ethnicity, to assess whether such differences contribute to severe maternal morbidity (SMM), and to estimate the contribution of antepartum anemia to SMM and nontransfusion SMM by race and ethnicity.

We conducted a population-based cohort study using linked vital record and birth hospitalization data for singleton births at or after 20 weeks of gestation in California from 2011 through 2020. Pregnant patients with hereditary anemias, out-of-hospital births, unlinked records, and missing variables of interest were excluded. Antepartum anemia prevalence and trends were estimated by race and ethnicity. Centers for Disease Control and Prevention criteria were used for SMM and nontransfusion SMM indicators. Multivariable logistic regression modeling was used to estimate risk ratios (RRs) for SMM and nontransfusion SMM by race and ethnicity after sequential adjustment for social determinants, parity, obstetric comorbidities, delivery, and antepartum anemia. Population attributable risk percentages were calculated to assess the contribution of antepartum anemia to SMM and nontransfusion SMM by race and ethnicity.

In total, 3,863,594 births in California were included. In 2020, Black pregnant patients had the highest incidence of antepartum anemia (21.5%), followed by Pacific Islander (18.2%), American Indian-Alaska Native (14.1%), multiracial (14.0%), Hispanic (12.6%), Asian (10.6%), and White pregnant patients (9.6%). From 2011 to 2020, the prevalence of anemia increased more than100% among Black patients, and there was a persistent gap in prevalence among Black compared with White patients. Compared with White patients, the adjusted risk for SMM was high among most racial and ethnic groups; adjustment for anemia after sequential modeling for known confounders decreased SMM risk most for Black pregnant patients (approximated RR 1.47, 95% CI 1.42-1.53 to approximated RR 1.27, 95% CI 1.22-1.37). Compared with White patients, the full adjusted nontransfusion SMM risk remained high for most groups except Hispanic and multiracial patients. Within each racial and ethnic group, the population attributable risk percentage for antepartum anemia and SMM was highest for multiracial patients (21.4%, 95% CI 17.5-25.0%), followed by Black (20.9%, 95% CI 18.1-23.4%) and Hispanic (20.9%, 95% CI 19.9-22.1%) patients. The nontransfusion SMM population attributable risk percentages for Asian, Black, and White pregnant patients were less than 8%.

Antepartum anemia, most prevalent among Black pregnant patients, contributed to disparities in SMM by race and ethnicity. Nearly one in five to six SMM cases among Black, Hispanic, American Indian-Alaska Native, Pacific Islander, and multiracial pregnant patients is attributable in part to antepartum anemia.