Background <p>Preterm premature rupture of membranes (PPROM) is a leading cause of preterm birth and neonatal morbidity, with inflammation playing a key role in its pathogenesis. This study aimed to evaluate the predictive value of the Systemic Immune-Inflammation Index (SII) and the Hemoglobin-Albumin-Lymphocyte-Platelet (HALP) score for perinatal outcomes and delivery timing in pregnancies complicated by PPROM.</p> Methods <p>This retrospective cross-sectional study included 317 pregnant women who were diagnosed with PPROM between 24 and 36 + 6 weeks gestation, from January 2018 to January 2024. SII and HALP scores were calculated from blood parameters at admission using the following formulas: SII = [platelets(/L) × neutrophils(/L)] / lymphocytes(/L) and HALP = [hemoglobin(g/L) × albumin(g/L) × lymphocytes(/L)] / platelets(/L). Neonatal outcomes (birth weight, APGAR scores, NICU admission) and delivery timing were analyzed. ROC curves and logistic regression models were used to assess predictive performance.</p> Results <p>Higher SII values were significantly associated with lower birth weights, lower 1- and 5-minute APGAR scores, and increased NICU admission. The SII showed modest predictive power for NICU admission (AUC: 0.653, cut-off = 1145.75) and strong discriminative ability for predicting delivery within 7 days (AUC: 0.860, cut-off: 1421, sensitivity and specificity: 78%). In contrast, the HALP showed limited and inconsistent discriminative performance and was not significantly associated with adverse outcomes. Multivariate logistic regression confirmed that the SII was as an independent predictor of NICU admission (<i>p</i> = 0.012).</p> Conclusion <p>The SII is a promising biomarker for predicting adverse neonatal outcomes and the timing of delivery in PPROM patients. A SII value &gt; 1421 may indicate delivery within 7 days, aiding in clinical management. Each 100-unit increase in SII was associated with an increased risk of NICU admission. The HALP score was not a reliable predictor.</p>