OBJECTIVE: In patients with a history of severe preeclampsia, an increased frequency of hemostatic abnormalities has recently been suggested in small studies without control groups. Our purpose was to investigate the prevalence of such abnormalities in a large patient group with a history of severe hypertensive disorder in pregnancy, in comparison with an appropriate control group. STUDY DESIGN: A total of 345 patients with a history of severe preeclampsia were investigated at a minimum of 10 weeks post partum for the presence of activated protein C resistance, the associated factor V mutation, hyperhomocysteinemia and anticardiolipin antibodies. The control group consisted of 67 healthy women with a history of uncomplicated pregnancies only. Blood was obtained during the second half of a normal menstrual cycle, and none of the patients or control subjects used oral contraceptives. RESULTS: Of all patients, 11.3% had activated protein C resistance (control subjects 1.5%, P =.025). Only half of these patients had the factor V mutation. Hyperhomocysteinemia was present in 12.1% of all patients, in comparison with 4.5% in the control group (P =.115). Anticardiolipin antibodies were observed in 20.9% of the patients, whereas these antibodies were found in 7.5% of the control subjects (P =.016). In general, the prevalence of these abnormalities was 1.5 to 2 times higher in patients who were delivered before 28 weeks, in comparison with patients who were delivered after 28 weeks. CONCLUSIONS: Hemostatic abnormalities, associated with an increased risk of thrombosis, are present in approximately 40% of patients with a history of severe preeclampsia, which is almost 4 times higher than in control subjects. These findings might suggest a cause of preeclampsia and could have implications in subsequent pregnancies and general health. http://www.ncbi.nlm.nih.gov/pubmed/10329869 van Pampus MG, Dekker GA, Wolf H, Huijgens PC, Koopman MM, von Blomberg BM, Büller HR.