Risk factors for peripartum anemia and blood transfusion: a two-center retrospective cohort study (2018-2020).

BACKGROUND: Peripartum anemia and transfusion contribute to maternal morbidity. While demographic and socioeconomic differences in anemia are known, gaps remain in how these relate to transfusion patterns across institutions. This study explored whether anemia prevalence and transfusion differed by site and patient context, and their association with sociodemographic factors. METHODS: This retrospective cohort included singleton deliveries ≥28 weeks at two Chicago hospitals (March 1, 2018 - February 29, 2020). 31,979 patients with third-trimester Hb values were included. Anemia was defined as Hb <11 g/dL and categorized as mild (9-10.9 g/dL), moderate (6-8.9 g/dL), or severe (<6 g/dL). The primary outcome was third trimester anemia; the secondary outcome was peripartum transfusion. Modified Poisson regression estimated adjusted risk ratios for anemia, and logistic regression estimated adjusted odds of transfusion. Analyses explored factors associated with these outcomes. RESULTS: Third-trimester anemia affected 12,841 patients (40.2%). Anemia was more common among non-Hispanic Black patients (53.3%), and lower-income neighborhood residents. Anemia was associated with younger age (adjusted risk ratio 0.99 per year), and delivery at University of Chicago (adjusted risk ratio 1.92). Transfusions occurred more frequently at Northwestern. In adjusted transfusion models, transfusion was associated with anemia severity, cesarean delivery, Hispanic ethnicity (adjusted odds ratio 1.62), and Asian race (adjusted odds ratio 1.42); non-Hispanic Black race was not (adjusted odds ratio 1.10). DISCUSSION: Anemia was more common among socioeconomically disadvantaged and non-Hispanic Black patients. Transfusion was associated with site, clinical factors, and anemia severity.