New ACR/EULAR 2023 classification criteria for antiphospholipid syndrome, what should a gynaecologist know in 2025

Antiphospholipid syndrome (APS) is characterised by thrombotic, obstetric and/or systemic manifestations associated with antiphospholipid antibodies (aPL). The definition of APS manifestations has been imprecise, resulting in heterogeneous study populations and in limited and inconsistent data, particularly for obstetric APS. In 2023, the American College of Rheumatology and the European League Against Rheumatism introduced new classification criteria that prioritize specificity over sensitivity. Obstetric APS manifestations are mainly the consequence of preeclampsia and placental insufficiency, often early and severe, leading to fetal growth restriction, fetal death, induced prematurity or maternal morbidity. Accordingly, in the new classification criteria, isolated fetal death without preeclampsia and/or placental insufficiency has little significance. The biological definition remains unchanged, requiring persistent aPL. Isolated anticardiolipin or anti-β2-glycoprotein-I antibodies of the IgM isotype or anticardiolipin or anti-β2-glycoprotein-I antibodies of the IgG isotype <40 GPL are no longer sufficient for the classification of APS due to their weak association with clinical manifestations. Lupus anticoagulant is the strongest risk factor for thromboses and adverse obstetric outcomes. Despite adequate treatment, pregnancies in these patients still carry a significant risk of preeclampsia, placental insufficiency, thrombosis and haemorrhagic events, those events being frequently associated and occurring mainly in the peripartum period, and in women with lupus anticoagulant. In the future, inclusion of individuals using these new classification criteria should ensure more homogeneity in APS trials, especially for obstetric APS. Importantly, these criteria were not designed for diagnosis, thus, in clinical practice, the risks and benefits of modifying the treatment of patients falling out of the 2023 criteria should be weighed by the clinicians (e.g. using aPL profile) and carefully explained to the patient.