The predictive value of systemic immune-inflammation index for clinical pregnancy achievement in recurrent implantation failure: A study of euploid frozen-thawed embryo transfer cycles

INTRODUCTION: To evaluate the association between the systemic immune-inflammation index (SII) measured on the day of embryo transfer (ET) and clinical pregnancy outcomes in patients with recurrent implantation failure (RIF) undergoing euploid frozen–thawed embryo transfer (FET) cycles.
METHODS: This retrospective cohort study included 160 RIF patients who underwent PGT-A-confirmed euploid blastocyst transfer between January 2022 and December 2024. SII was calculated as platelet count × (neutrophil count / lymphocyte count) using blood samples obtained on the morning of ET. Multivariable logistic regression and receiver operating characteristic (ROC) curve analyses were performed to evaluate predictive factors
RESULTS: Clinical pregnancy was achieved in 29.4% (47/160) of patients. SII levels were lower in patients with clinical pregnancy compared to those without (321.4 ± 115.0 vs. 448.6 ± 166.8; p=0.009). Each 100-unit decrease in SII was independently associated with an increased likelihood of clinical pregnancy (OR: 1.29; 95% CI: 1.03–1.62; p=0.025). ROC analysis identified an optimal cut-off value of 380 (AUC=0.68). Clinical pregnancy rates were higher in the low SII group (<380) compared to the high SII group (40.3% vs. 20.5%; p=0.009).
DISCUSSION AND CONCLUSION: SII measured on the day of ET is an independent predictor of clinical pregnancy in euploid FET cycles among RIF patients and may serve as a practical, non-invasive marker for risk stratification.

Keywords: Recurrent implantation failure, Systemic immune-inflammation index, Euploid embryo transfer, Frozen-thawed embryo transfer