Objective: The objective of the study was to investigate the potential role of impaired factor XII-dependent activation of fibrinolysis in treated antiphospholipid syndrome gestations developing late-pregnancy complications. Study design: This was a prospective study in a third-level teaching hospital, including 75 patients: 25 pregnant patients having the antiphospholipid syndrome and carrying their pregnancies until 26 weeks’ gestation or later (group 1); 25 pregnant patients having normal term pregnancies and delivery and no previous miscarriage (group 2); and 25 pregnant patients being diagnosed as having severe pre- eclampsia and/or intrauterine growth restriction but testing negative for antiphospholipid antibodies (group 3). Hemostatic evaluation was carried out from patients in groups 1 and 2 between 6 and 10 weeks, between 18 and 22 weeks, and between 28 and 32 weeks’ gestation. Patients in group 3 were sampled between 28 and 32 weeks. An additional blood sample was obtained 4 to 6 months after delivery (baseline). The Mann-Whitney U test, the Friedman test, and the χ 2 test were used. Results: Patients in group 1 were characterized by increased factor VIIa levels, increased prothrombin fragment 1+ 2 levels, reduced factor XIIa levels, diminished functional urokinase-type plasminogen activator levels, and decreased levels of plasmin/alpha- 2-plasmin inhibitor complexes. These abnormalities were more evident in patients in group 1 developing pre-eclampsia and/or intrauterine growth restriction. Conclusions: Impaired factor XIIa-dependent activation of fibrinolysis seems to be a key mechanism related to late pregnancy complications in patients with the antiphospholipid syndrome. Objective: The objective of the study was to investigate the potential role of impaired factor XII-dependent activation of fibrinolysis in treated antiphospholipid syndrome gestations developing late-pregnancy complications. Study design: This was a prospective study in a third-level teaching hospital, including 75 pregnant women having the antiphospholipid syndrome and carrying their pregnancies until 26 weeks’ gestation or later (group 1); 25 pregnant patients having normal term pregnancies and delivery and no previous miscarriage (group 2); and 25 pregnant patients being diagnosed as having severe pre-eclampsia and / or intrauterine growth restriction but testing negative for antiphospholipid antibodies (group 3). Hemostatic evaluation was carried out from patients in groups 1 and 2 between 6 and 10 weeks, between 18 and 22 weeks, and between 28 and 32 weeks’ gestation. Patients in group 3 were sampled between 28 and 32 weeks. An additional blood sample was obtained 4 The Mann-Whitney U test, the Friedman test, and the χ 2 test were used. Results: Patients in group 1 were characterized by increasing factor VIIa levels, increased prothrombin fragment 1 + 2 levels, reduced factor XIIa levels, diminished functional urokinase-type plasminogen activator levels, and decreased levels of plasmin / alpha-2-plasmin inhibitor complexes. These abnormalities were more evident in patients in group 1 developing pre-eclampsia and / or intrauterine growth restriction. Conclusions : Impaired factor XIIa-dependent activation of fibrinolysis seems to be a key mechanism related to late pregnancy complications in patients with the antiphospholipid syndrome.