Maternal morbidity in postpartum severe preeclampsia by obstetric delivery volume.

Background: Pre-eclampsia is a leading cause of maternal morbidity and mortality in the United States. Emerging data suggests that postpartum pre-eclampsia may be associated with a higher incidence of maternal morbidity compared to hypertensive disorders of pregnancy (HDP) diagnosed antenatally. Understanding postpartum maternal risk across facilities with a spectrum of obstetric services is critical with the rising rates of pre-eclampsia in all healthcare settings.

Objectives: We investigated the relationship between facility delivery volume and rates of non-transfusion severe maternal morbidity (SMM) among patients readmitted postpartum for pre-eclampsia with severe features.

Study design: This is a retrospective cohort study using the Nationwide Readmissions Database (2015-2019) of postpartum patients readmitted for pre-eclampsia with severe features. Our primary outcome was non-transfusion SMM during readmission, defined per U.S. Centers for Disease Control and Prevention criteria. We also evaluated SMM, cardiac SMM, and individual morbidities. The exposure variable was the number of annual deliveries at the readmitting facility. Restricted cubic splines with 4 knots were used to assess the functional form of the relationship between obstetric delivery volume and non-transfusion SMM; a linear relationship was identified as optimal. Logistic regression was used to estimate adjusted odds ratios (aOR) which controlled for maternal age, non-transfusion SMM at delivery, expanded obstetric comorbidity index, and HDP during delivery.

Results: The cohort included 29,472 patients readmitted with postpartum pre-eclampsia with severe features. The primary payer was 55% private and 42% governmental. Median age was 31.4 years. Most patients did not have prior HDP (65%) or chronic hypertension (86%) diagnosis antenatally. The median interval from delivery hospitalization to readmission was 3.9 days (25^th percentile-75^th percentile: 2.2-6.5). Non-transfusion SMM occurred in 7% of patients readmitted to facilities with >2,000 deliveries compared to 9% with 1-2,000 deliveries, and 52% without any delivery hospitalizations. The most common SMM was pulmonary edema and heart failure, observed in 4% of readmissions. We observed that for every increase in 1,000 deliveries, the odds of a non-transfusion SMM at readmission decreased by 3.5% (aOR: 0.965; 95% confidence interval: 0.94, 0.99) CONCLUSIONS: Non-transfusion SMM for postpartum readmissions with pre-eclampsia with severe features was inversely associated with readmitting hospital delivery volume. This information may guide risk-reducing initiatives for identifying strategies to optimize postpartum care at facilities with lower or no delivery volume.