ABSTRACTBackgroundThe objective of this study was to investigate the clinical relevance of anti‐prothrombin antibodies (aPT) and anti‐phosphatidylserine/prothrombin antibodies (aPS/PT) in relation to pregnancy outcomes and coagulation parameters, as well as immune markers.MethodsWe retrospectively analyzed 477 pregnant women with experienced at least one spontaneous miscarriage who were tested for aPT and aPS/PT antibodies, and compared their clinical characteristics, coagulation indicators, immune biomarkers, and pregnancy outcomes to assess the diagnostic accuracy of these antibodies.ResultsWe found that the aPT IgG and the aPS/PT IgM were independently associated with increased risk of pregnancy loss, with odds ratios (ORs) of 1.055 (95% confidence interval [CI]: 1.009–1.103, p = 0.017) and 1.041 (95% CI: 1.015–1.067, p = 0.002), respectively. Moreover, we found that the aPS/PT IgM had a higher diagnostic performance than the aPT IgG, as indicated by the AUC of 0.663 and 0.593, respectively. The pregnancy loss rate was positively correlated with the level of aPS/PT IgM, while the aPT IgG is not. We also found that in the pregnancy loss group, aPT IgG showed negative correlations with prothrombin time (PT); aPS/PT IgM showed positive correlations with aPS/PT IgG. However, none of aPT IgG, aPT IgM, aPS/PT IgM, or aPS/PT IgG was related to other adverse pregnancy outcomes, such as preterm delivery, fetal growth restriction (FGR), or preeclampsia (PE).ConclusionOur findings suggest that aPT IgG and aPS/PT IgM are independent risk factors for pregnancy loss, especially aPS/PT IgM, which has a positive linear correlation with pregnancy loss.