FRI0349 Low titer anti-phospholipid antibodies convey an increased obstetric risk
Authors: C.B. Chighizola, F. Pregnolato, M.G. Raimondo, C. Comerio, C. Sobrino Grande, L. Trespidi, M.O. Borghi, M. Gerosa, B. Acaia, M.W. Ossola, A. Bulfoni, P.L. Meroni
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Persistent positivity for anti-phospholipid antibodies (aPL) at medium-high titres is required to diagnose anti-phospholipid syndrome (APS), an autoimmune condition characterised by thrombosis and/or pregnancy morbidity (PM). However, increasing evidence points towards the clinical relevance of low titre aPL in obstetric APS. <h3>Objectives</h3> This study investigated the association of low titre aPL with PM assessing the efficacy of low-dose aspirin (LDASA) and low-molecular weight heparin (LMWH). <h3>Methods</h3> Data on pregnancies in women with persistent aPL positivity at any titre were retrospectively collected at a single centre. An association model for repeated measures was applied to quantify the obstetric risk conveyed by low titre and criteria aPL, allowing to: i) evaluate pregnancy outcomes over time using available longitudinal data; ii) account that pregnancies of the same woman are not independent events; iii) consider that women had a different number of pregnancies; iv) estimate the role of several confounders and predictors. The association model envisaged as dependent variable pregnancy outcome as a binary outcome, defined for each pregnancy as "obstetric complication yes <i>versus</i> no" (pregnancy loss before 10 weeks, pregnancy loss after 10 weeks, premature birth before 34 weeks, according to updated APS classification criteria [Miyakis et al]). <h3>Results</h3> One hundred eleven women were recruited in this study: 160 pregnancies in women with low titer aPL and 178 pregnancies in women eith criteria aPL. According to the association model, women with low titre aPL had a probability of PM of 63% (odds 1.72, 95% CI 1.05–2.80) in case of single positivity and of 79% (odds 3.78, 95% CI 1.96–7.30) in case of double positivity. Criteria aPL conveyed a 2.2-fold higher risk: the probability of PM was 79% in case of single positivity (odds 3.82, 95% CI 2.15–6.80), raising to 89% (8.41, 95% CI 3.99–17.73) for multiple aPL. LDASA-treated women with single low titer aPL positivity had a 16% probability of exeriencing an adverse outcome (odds 0.19, 95%IC 0.08–0.44) while LDASA did not significantly affect the probability of in patients with low titre double aPL positivity (odds 0.42, 95%IC 0.17–1.02). Similarly, LDASA significantly reduced PM among women with single, but not multiple, criteria aPL positivity (odds 0.42, 95% CI 0.19–0.94; odds 0.93, 95% CI 0.39–2.21). Among women treated with LDASA +LMWH, the probability of PM was 14% in case of single low titre aPL positivity (odds 0.17, 95%IC 0.08–0.37) and 28% in case of two low titre aPL (odds 0.38, 95%IC 0.18–0.80). Among women with aPL criteria, treatment with LDASA +LMWH reduced the probability of PM to 28% (odds 0.38, 95%IC 0.21–0.70) in case of a single positive test and, not significantly, to 45% (odds 0.84, 95%IC 0.45–1.55) in case of multiple positivities. <h3>Conclusions</h3> Low titre aPL are associated with PM; the association treatment with LDASA and LMWH is effective even among women with low titre aPL. The risk of PM and the response to treatment depend upon aPL profile, suggesting the importance of a tailored treatment. <h3>Disclosure of Interest</h3> None declared