Thrombophilia and adverse pregnancy outcome.

The hemostatic system plays an important role in three crucial stages of pregnancy: ovulation, implantation, and placentation. A thrombophilic defect is an abnormality in the coagulation pathways that predisposes an individual to thrombosis. Pregnancy is a hypercoaguable state and interest has focused on the potential role that thrombophilic defects may play in the etiology not only of recurrent miscarriage but also of late pregnancy complications. Maternal intervillous blood flow does not develop to any significant extent before 8 weeks of gestation and thrombophilic defects are therefore unlikely to contribute to pregnancy loss before this time. Retrospective studies have reported a similar prevalence of genetic thrombophilic defects among women with recurrent first-trimester miscarriage and controls but an increased prevalence among those with second-trimester miscarriage and later pregnancy complications. There is a paucity of data documenting the prospective outcome of untreated pregnancies among women with thrombophilic defects and of the placental histology in these pregnancies. Until these issues have been addressed, routine thromboprophylaxis during pregnancy cannot be recommended for women with thrombophilic abnormalities.