Treatment of pregnant women with antiphospholipid syndrome (APS) should be set apart from that from thrombotic APS patients. Patients with a history of pregnancy morbidity but no vascular thrombosis are usually treated with a prophylactic dose of heparin plus low-dose aspirin; whereas, those with previous vascular thrombosis alone or associated with previous pregnancy morbidity, are commonly treated with a therapeutic dose of heparin generally combined with low-dose aspirin. However, in about 20% of pregnant APS women these regimens fail. In this context, we conducted a case-control study on a large multicentre cohort of conventionally treated pregnancies to verify whether specific laboratory profiles and/or clinical characteristics are predictive of unsuccessful pregnancy outcome during conventional treatments. Multivariate analysis showed that pregnancy failure during conventional therapies was independently associated with a history of both thrombosis and pregnancy morbidity, the presence of systemic lupus erythematosus (SLE) or other systemic autoimmune diseases and triple antiphospholipid antibody positivity. With the aim to discover the most effective and safe treatments in high-risk pregnant APS women a large-scale multicentre study focusing on the effect of treatments on pregnancy outcome in women with APS and further risk factors for pregnancy failure has been designed.