Prognostic value of lupus anticoagulant and anti‐β2 glycoprotein I antibody in adverse pregnancy outcomes.

Objective International criteria for antiphospholipid syndrome (APS) include lupus anticoagulant (LA), anticardiolipin (aCL) immunoglobulin (Ig) G and IgM, and anti‐β2‐glycoprotein I (β2GPI) IgG and IgM. However, evidence supporting their prognostic value or treatment efficacy in improving live birth rates is limited. The Lancet series on miscarriage recommends testing only for LA and aCL, excluding β2GPI. We aimed to examine whether commercially available antiphospholipid antibody (aPL)‐related tests have a prognostic value for obstetric APS. Methods This prospective cohort study enrolled 1,237 pregnant women between July 2021 and March 2024. Women using heparin, including those with an obstetric APS diagnosis before pregnancy, were excluded. Pregnancy outcomes were followed until December 2024. The aPL‐related tests comprised LA (diluted activated partial prothrombin time and diluted Russell's viper venom time (LA‐RVVT)), aCL IgG, IgM, anti‐β2GPI IgG, IgM, anti β2GPI domain I IgG, phosphatidylserine‐dependent anti‐prothrombin (aPS/PT) IgG, IgM, protein S, and coagulation factor XII activity. Results The prevalence rates of early‐onset preeclampsia, intrauterine fetal death (IUFD), and small gestational age were 1.4% (17), 0.7% (9), and 0.9% (11), respectively. Logistic regression analysis revealed that LA‐RVVT and anti‐β2GPI IgG were each predictor of early‐onset preeclampsia and IUFD. The area under the curve for these conditions increased to about 0.8 when combined with a history of preeclampsia or IUFD, respectively. Conclusion LA‐RVVT, anti‐β2GPI IgG, complications including hypertension and a history of IUFD were valuable in identifying obstetric APS. The variation in test results across facilities limits the ability to establish consistent prognostic or treatment value for each aPL.