Predictive Value of Blood-Derived Inflammatory Markers for Histologic Chorioamnionitis in Preterm Premature Rupture of Membranes

Background: Chorioamnionitis is a significant contributor to adverse maternal and neonatal outcomes in pregnant women with preterm premature rupture of membranes (PPROM). This study explored the predictive value of several blood-derived inflammatory indices for histologic chorioamnionitis (HCA) in PPROM. Methods: Pregnant women with PPROM admitted between July 2017 and July 2025 were retrospectively included. According to postpartum placental pathology, patients were classified into an HCA group (n = 45) and a non-HCA group (n = 152). Clinical characteristics and laboratory indices were compared, including the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), lymphocyte-to-monocyte ratio (LMR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), and neutrophil-to-platelet ratio (NPR). Receiver operating characteristic (ROC) curve analysis was used to evaluate diagnostic performance. Univariate and multivariable logistic regression analyses identified independent predictors of HCA. Results: Compared with the non-HCA group, the HCA group had an earlier gestational age at rupture (≤34 weeks: 51.11% vs. 19.08%, p < 0.001) and a higher incidence of low birth weight (<2.5 kg: 60.00% vs. 32.24%, p < 0.001). White blood cell count (WBC), neutrophil count, C-reactive protein (CRP), NLR, PLR, SII, and SIRI were significantly higher in the HCA group, whereas LMR was lower. Among all indices, SIRI showed the largest area under the ROC curve (AUC = 0.727) and remained independently associated with HCA after adjustment. Conclusions: SIRI is a simple, noninvasive marker derived from routine blood counts and showed the best discriminatory performance for HCA among the tested indices. Its clinical utility should be validated in prospective, multicenter studies before being implementation in clinical decision-making.