Background/Objectives: Complete blood count inflammatory indices are widely studied in obstetrics but rarely compared directly. We compared five first-trimester indices, the systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), pan-immune-inflammation value (PIV), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR), for their associations with preterm birth, examined across its severity. Methods: In a retrospective single-centre cohort of 5003 singleton pregnancies with a first-trimester complete blood count, late (34–36 weeks) and early (<34 weeks) preterm births were analysed separately. The association of each index with preterm birth was assessed by logistic regression, per standard deviation, and by quartile, with adjustments made for maternal age, body mass index, parity, fetal sex, and gestational age at sampling; discrimination was compared using the DeLong test. The birthweight category, classified against the INTERGROWTH-21st standards, was a secondary outcome. Results: After adjustment, all indices except for the PLR were associated with preterm delivery, with similar effects per standard deviation. Among the five indices, the SIRI showed the most consistent association with the severity of preterm birth: its values rose at every step from term to late to early birth. It discriminated these births best (area under the curve 0.600, significantly greater than the SII), and its quartile gradient was steepest, with the odds more than doubling from the lowest to the highest quartile. All five remained weak discriminators, with every area under the curve being below 0.70, and none was associated with the birthweight category. Conclusions: These indices are not standalone predictive tests, but among them, the SIRI, which, unlike the SII, captures the monocyte count, was most closely associated with early, more severe preterm birth, consistent with the role of monocytes in the inflammation of labour.

Background: Cervical cerclage reduces the risk of preterm birth, but factors associated with its success may not be uniform. Among singleton pregnancies with ultrasound- or physical examination-indicated cerclage (no history-based indication), we examined whether factors associated with delivery differ by gestational-age threshold. Methods: This single-center historical cohort included 114 women undergoing cerclage between May 2020 and December 2025: ultrasound-indicated with cervical length 10 to < 20 mm (Group 1, n = 41) or < 10 mm (Group 2, n = 32), and physical examination-indicated cervical dilatation (Group 3, n = 41). All cerclages used the McDonald technique with polypropylene monofilament suture. The primary outcome was gestational age at delivery, assessed at ≥ 34, < 32, and < 28 weeks. Firth penalized multivariable logistic regression evaluated study group, maternal age, and gestational age at cerclage as primary covariates; post-cerclage cervical length was analyzed separately as a secondary post-treatment-adjusted variable. All models were exploratory, and p values were nominal. Results: In these exploratory models, factors associated with delivery differed across thresholds. For delivery ≥ 34 weeks, gestational age at cerclage was the only covariate independently associated with the outcome (aOR 1.28 per week, 95% CI 1.04 to 1.59; p = 0.021). For delivery before 32 weeks (aOR 2.96, 95% CI 1.08 to 8.66; p = 0.034) and before 28 weeks (aOR 9.36, 95% CI 1.98 to 91.11; p = 0.003), physical examination-indicated cerclage was the only covariate that reached significance; 11 of the 14 deliveries before 28 weeks occurred in this group, so this estimate is imprecise and near-separating. The numerically higher rate of delivery ≥ 34 weeks in Group 2 than Group 1 (78.1% vs. 70.7%) was not statistically significant. Apparent discrimination was moderate (AUC 0.69 to 0.77), without internal validation. Conclusions: In this exploratory single-center cohort, the factors associated with delivery varied with the gestational-age threshold examined. Near term, later gestational age at cerclage was associated with delivery ≥ 34 weeks; at earlier thresholds, physical examination-indicated cerclage identified a higher-risk group for very and extreme preterm delivery, although these estimates were imprecise and partly confounded by indication severity and co-interventions. Findings should be interpreted as hypothesis-generating and require confirmation in larger prospective studies.