In this population-based case-control study we explored the association of antiphospholipid antibodies with pregnancy-related venous thrombosis. From 1990 through 2003 615 pregnant women were identified at 18 hospitals in Norway with a diagnosis of first time VT. In 2006, 531 of 559 eligible cases and 1092 of 1229 eligible controls were invited for further investigations. The final study population comprised 313 cases and 353 controls, who completed a comprehensive questionnaire and donated a single blood sample, 3-16 years after index pregnancy. We report the results on lupus anticoagulant, anticardiolipin antibodies, and anti-ss(2) glycoprotein-1 antibodies alone, in combination, and with the contribution of the factor V Leiden and the prothrombin gene G20210A polymorphisms. Cut-off values for APAs were chosen according to current international consensus. 29 (9.3%) of the cases and 24 (6.8%) of the controls had at least one positive test for APAs (OR 1.4; 95% CI 0.8-2.5). Nine cases (2.8%) and no controls had more than one positive test (multi-positivity) for APAs. After excluding women with factor V Leiden or prothrombin polymorphisms, still 6 cases were multi-positive for APAs. We conclude that multi-positivity, but not single-positivity, for APAs was weakly associated with a history of ante- and postnatal VT.
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