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Racial/Ethnic Differences in Pre-Pregnancy Conditions and Adverse Maternal Outcomes in the nuMoM2b Cohort

Background: Adverse maternal outcomes and multimorbidity affect a growing proportion of pregnant individuals in the United States and with racial and ethnic disparities in the rates of multimorbidity. There is limited research on multimorbidity, measured as the co-occurrence of two or more chronic conditions, and how it impacts adverse maternal outcomes. Objectives: We sought to: (1) determine how pre-pregnancy conditions and their combined effects contribute to racial disparities in adverse maternal outcomes; and (2) incorporate conditions and their combined effects into predictive modeling algorithms to improve risk prediction using information available in the first trimester, specifically for racial minority subgroups. Study Design: We used data from the 'Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be' (nuMoM2b) observational cohort study. We defined multimorbidity as the co-occurrence of two or more pre-pregnancy conditions. The primary outcomes of interest were severe preeclampsia, postpartum readmission, and blood transfusion during pregnancy or up to 14 days postpartum. We used weighted Poisson regression with robust variance to estimate adjusted risk ratios and 95% confidence intervals, and we used mediation analysis to evaluate the contribution of the combined effects of pre-pregnancy conditions to racial/ethnic disparities. We also evaluated the performance of our models by racial subgroup using the area under the receiver operating characteristic curve (AUC) metric. Results: In the nuMoM2b cohort (n=8729), 3.6% (n=318) experienced severe preeclampsia, 1.8% (n=157) experienced blood transfusion, and 1.8% (n=154) experienced postpartum readmission. 22.8% of all participants experienced two or more co-occurring pre-pregnancy conditions. Cardiovascular conditions were associated with an increased relative risk for severe preeclampsia (aRR, 1.71; CI, 1.59-1.84), and this risk was additionally exacerbated when hematologic conditions were co-occurring with cardiovascular conditions (aRR, 1.34; CI, 1.12-1.60). The mediation analysis results were not statistically significant; however, cardiovascular conditions explained 36.6% of non-Hispanic Black individuals' association with increased risk for severe preeclampsia (p=0.07). The addition of pre-pregnancy conditions increased AUC for the prediction of blood transfusion and severe preeclampsia, and moreover, the multiracial subgroup experienced the greatest improvement in predictive performance of blood transfusion due to this addition (an increase in AUC 0.51 to 0.69). The best subgroup performance was in predicting severe preeclampsia in multiracial individuals using confounders and condition types, with an AUC of 0.74. Conclusion: Though there is a greater burden of some pre-pregnancy conditions and co-occurring conditions among minority individuals, these conditions alone do not fully explain the higher rates of adverse maternal outcomes. However, some conditions and their combined effects are associated with adverse maternal outcomes. The incorporation of pre-pregnancy multimorbidity improves the performance of some risk prediction models, especially for correctly classifying individuals of minority race.