Abstract
BACKGROUND: Preeclampsia (PE) is a pregnancy-specific hypertensive disorder linked to systemic inflammation. The systemic immune-inflammation index (SII), calculated from neutrophil, lymphocyte, and platelet counts, has emerged as a novel immune activation marker. Its longitudinal changes in pregnancy and predictive performance for adverse outcomes in PE are not well established. METHODS: This retrospective cohort study included 692 clinical records of women with PE who delivered at Shanghai First Maternity and Infant Hospital between January 2019 and June 2024, representing 685 unique patients, 7 of whom delivered twice. SII, systemic inflammatory response index (SIRI), other inflammatory indices, and biochemical parameters were measured at four time points: the first, second, and third trimesters, and the postpartum. Linear mixed-effects models evaluated longitudinal trends, and random intercepts were used as predictors in logistic regression models assessing adverse pregnancy outcomes. All two-and three-biomarker combinations were evaluated, and DeLong's test (α = 0.05) was used to compare the area under the Receiver Operating Characteristic (ROC) curves and AUC values of each combination with that of the best single-biomarker model. RESULTS: Among the 692 records of women with PE, 204 (29.5%) experienced adverse pregnancy outcomes. SII showed an overall increasing trend during pregnancy and demonstrated moderate predictive performance (AUC = 0.666). The combination model including SII, alanine transaminase (ALT), and creatinine (Cr) achieved the highest predictive performance (AUC = 0.712, 95% CI: 0.669-0.755, P = 0.011), outperforming each single-biomarker. CONCLUSION: SII followed an overall increasing trend during pregnancy in patients with PE and was associated with adverse pregnancy outcomes. Combining SII with ALT and Cr improved predictive performance and may be a practical tool for clinical monitoring and early intervention.