First-Trimester CBC-Derived Inflammatory Indices for Prediction of Miscarriage: A Retrospective Cohort Study.

OBJECTIVE: To develop and internally validate a predictive model for miscarriage using clinical factors combined with CBC-derived inflammatory indices, including the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), and systemic inflammation response index (SIRI). METHODS: This retrospective cohort study included Thai women with singleton pregnancies who attended their first antenatal visit during the first trimester between January 2020 and December 2025. Eligible participants had available CBC results and pregnancy outcomes. Associations between CBC-derived indices and subsequent miscarriage were evaluated, and predictive models were developed. Model discrimination was assessed using the area under the curve (AUC). RESULTS: A total of 796 women were included, comprising 118 with subsequent miscarriage and 678 with ongoing pregnancies. Gestational age was significantly lower among the study group (7.32 ± 1.61 vs. 8.69 ± 2.07 weeks, p < 0.001). Women who miscarried had significantly higher lymphocyte counts but lower neutrophil counts and NLR than controls. A clinical model based on maternal age and gestational age demonstrated modest discrimination (AUC, 0.741). A penalized model incorporating maternal age, gestational age, NLR, and SII significantly improved predictive performance (AUC, 0.781; p = 0.001). At a predicted probability threshold of 0.15, the model achieved a sensitivity of 77.1% and a specificity of 70.0%. CONCLUSION: Maternal age and gestational age were significant predictors of miscarriage, and the first-trimester combination model provided significant improvement in discrimination. Because these indices are routinely derived from standard CBC testing without additional cost, they may potentially serve as practical adjuncts to clinical risk factors for early miscarriage risk stratification after validation.