A thrombophilic defect is an abnormality in the coagulation system that predisposes an individual to thrombosis. This chapter examines the role that the acquired thrombophilic defects play in the magnitude of early pregnancy loss, with particular reference to Primary Antiphospholipid syndrome, hyperhomocysteinemia and Acquired protein C resistance. Antiphospholipid syndrome (APS) is now recognized to be the most important treatable cause of recurrent miscarriage. The potential of thromboelastography as a clinical tool to overcome many of the above limitations in hemostasis testing in our recurrent pregnancy-loss population is promising. The success of thromboprophylactic treatment for women with recurrent miscarriage associated with APS has resulted in women with unexplained recurrent miscarriage frequently demanding similar treatment. Recurrent miscarriage is a distressing condition that affects at least 1% of couples trying to achieve a successful pregnancy. Recurrent miscarriage is a heterogeneous condition and no single abnormality will account for all cases.