Assessing the sensitivity and the clinical impact of the 2023 ACR/EULAR classification criteria in Obstetric Antiphospholid Syndrome: findings from a multicenter Italian cohort with a long-term follow-up

Objective: To evaluate the sensitivity of the 2023 ACR/EULAR classification criteria for antiphospholipid syndrome (APS) in a real‐world cohort of women diagnosed with primary obstetric APS (oAPS), and to assess their ability to identify patients at risk of future pregnancy complications. Methods: We conducted a multicenter retrospective study on women diagnosed with primary oAPS by expert rheumatologists between 2006 and 2023 in two Italian rheumatology centers. All patients were retrospectively classified using both the 2006 Sydney and the 2023 ACR/EULAR classification criteria. Follow‐up at 1 and 5 years after clinical diagnosis was analyzed to identify new obstetric events and assess associations with baseline classification status. Results: Our cohort included 122 women. At baseline, 75.4% of patients fulfilled the Sydney criteria, and 23% met the 2023 ACR/EULAR criteria. The main reasons for exclusion under the 2023 ACR/EULAR criteria were insufficient clinical score due to isolated fetal losses (56.4%), insufficient laboratory score due to isolated IgM aPL positivity (4.3%), or a combination of both (5.3%). During five years of follow‐up, more than one‐quarter of the patients who became pregnant experienced new obstetric events. The majority of these cases did not fulfill the 2023 ACR/EULAR criteria. Conclusion: The 2023 ACR/EULAR classification criteria demonstrate low sensitivity (23%) in women with primary oAPS and fail to identify those at risk of future events. These findings underscore the need for cautious clinical judgment in managing oAPS: misuse of these criteria may result in undertreatment and increase the risk of recurrent obstetric complications.