Non-Criteria Antiphospholipid Antibodies in Women with Recurrent Pregnancy Loss

Background: Recurrent pregnancy loss (RPL) remains etiologically unexplained in 40–50% of cases following standard diagnostic workup. Non-criteria antiphospholipid antibodies (non-criteria aPL) are increasingly considered potential markers of seronegative obstetric antiphospholipid syndrome (APS); however, their diagnostic value in this clinical setting requires further investigation. Objective: To assess the diagnostic value of non-criteria aPL in women with RPL and to construct an exploratory immunological scoring model for diagnostic stratification. Methods: Antiphospholipid antibody detection was performed using a single-measurement semi-quantitative line immunoblot assay (Anti-Phospholipid 10 Dot, Generic Assays, Germany). Statistical analysis included χ2, Fisher’s exact test, Mann–Whitney U test, binary logistic regression, and ROC analysis. Results: Statistically significant associations with RPL were observed for anti-prothrombin antibodies (OR = 11.1; 95% CI 1.8–68.0; p = 0.022 Haldane–Anscombe correction), anti-annexin V (OR = 4.28; 95% CI 1.18–15.6; p = 0.023), and anti-β2GP I (OR = 3.31; 95% CI 1.18–9.28; p = 0.019). The exploratory composite immunological score demonstrated moderate discriminatory performance (AUC = 0.701; 95% CI 0.588–0.814; p = 0.005). The overall logistic regression model was statistically significant (χ2 = 8.564; p = 0.036), although none of the individual predictors retained independent significance, indicating a contribution of cumulative immunological burden rather than any single marker. Conclusions: In this single-center cross-sectional study, non-criteria aPL were frequently detected in women with RPL and were statistically associated with the condition. The findings should be interpreted as hypothesis-generating only, given the cross-sectional design, single-measurement immunoblot, small control group, and absence of external validation. Confirmation in larger prospective multicenter cohorts using ELISA-based assays with the internationally recommended 12-week repeat measurement is required before any clinical implementation.