 Although most pregnancy losses occur in the first trimester, women with thrombophilia are at an increased risk for pregnancy loss in the second and third trimesters. A number of studies found that FVL carriers have a significantly higher risk of late pregnancy loss than early first trimester loss Sarig 2002; Meinardi 1999. One possible explanation is that late pregnancy losses may reflect thrombosis of placental vessels. However, the majority of pregnancy losses in women with thrombophilia still occur in the first trimester Sarig 2002; Younis 2000. The mechanisms responsible for the association of inherited thrombophilia with RPL have not been fully elucidated. Pathological studies of placentas obtained from gestations terminated by foetal loss reveal thrombotic changes and infarcts. These can be observed at the maternal vessels in 50-90 of placentae of women with stillbirth Gris 1999; Many 2001. However, these changes can also be found in a significant proportion of women with RPL without thrombophilia Gris 1999; Martinelli 2000. Raising the possibility of yet undetermined gestational prothrombotic risk factors either at fetal vessels or at maternal vessels. A role for foetoplacental thrombosis has been suggested by studies demonstrating an association between factor V genotype in miscarried foetuses and placental infarction. However, the findings of thrombotic changes at the maternal side and the efficacy of LMWH, which do not cross the placentae, in preventing foetal loss are in support with the latter. Emerging data on therapy of women with inherited thrombophilia and pregnancy loss is mostly uncontrolled and include small series of patients treated mainly with LMWH. The potential advantages of LMWH over unfractionated heparin are higher antithrombotic ratio, meaning less bleeding for better antithrombotic effect, longer half-life with a potential need for only one injection per day, smaller injected volume and less heparin-induced thrombocytopenia. These advantages are particularly appealing for prolonged prophylaxis throughout pregnancy and the postpartum period. A recent collaborative study has demonstrated the safety of using LMWH during 486 gestations Sanson 1999. Successful outcome was reported in 8393 89 gestations in women with recurrent pregnancy loss and in all 28 gestations in women with preeclampsia in previous pregnancy. 