PROS1 and Venous thrombosis: A higher risk of spontaneous abortion in women with these deficiencies has been reported.33 Since protein C deficiency can affect 10 to 15% of young individuals with recurrent venous thrombosis20 and protein S deficiency occurs in 2.2% of patients with venous thrombosis,15 we investigated whether thrombosis at an implantation site could lead to recurrent abortion in women with these deficiencies.