Objective To investigate whether patients having antiphospholipid syndrome (APS) as the only aetiological factor for recurrent spontaneous abortion (RSA) are at increased risk of thrombosis later in life.

Methods A case–control study at a tertiary university referral centre. The study group consisted of 57 primary APS and RSA women (APS–RSA group). Control groups included: 86 patients with RSA of unknown aetiology (uRSA group), 42 patients with RSA and thrombophilic genetic defects as the only aetiologic factor for RSA (tRSA group) and 30 antiphospholipid antibody (aPL) positive but otherwise healthy women (aPL group). The main measurement was the thrombosis rate after long-term follow-up.

Results APS–RSA patients had a significantly higher 12-year cumulative thrombotic incidence rate compared with the three comparator groups (19.3% vs 4.8%, 0.0% and 0.0%, respectively (log rank), p<0.001). Patients in the APS–RSA group had 25.6 thrombotic events per 1000 patient-years (95% CI 12.8 to 45.9). The OR of thrombosis in relation to the presence (APS–RSA group) or absence (uRSA and tRSA groups) of aPL in patients with RSA was 15.06 (95% CI 3.2 to 70.5).

Conclusions Our data indicate that a history of RSA associated with aPL is a risk factor for subsequent thrombosis in the long term.