Thrombophilia is not associated with an increase in placental abnormalities in women with intra-uterine fetal death

Heparin rescues factor V Leiden-associated placental failure independent of anticoagulation in a murine high-risk pregnancy model

Low molecular weight heparin (LMWH) is being tested as an experimental drug for improving pregnancy outcome in women with inherited thrombophilia and placenta-mediated pregnancy complications, such as recurrent pregnancy loss. The role of thrombotic processes in these disorders remains unproven, and the issue of antithrombotic prophylaxis is intensely debated. Using a murine model of factor V Leiden-associated placental failure, we show that treatment of the mother with LMWH allows placental development to proceed and affords significant protection from fetal loss. Nonetheless, the therapeutic effect of LMWH is not replicated by anticoagulation; fondaparinux and a direct Xa inhibitor, C921-78, achieve anticoagulation similar to LMWH but produce little or no improvement in pregnancy outcome. Genetic attenuation of maternal platelet aggregation is similarly ineffective. In contrast, even a partial loss of thrombin sensitivity of maternal platelets protects pregnancies. Neonates born from these pregnancies are growth retarded, suggesting that placental function is only partially restored. The placentae are smaller but do not reveal any evidence of thrombosis. Our data demonstrate an anticoagulation-independent role of LMWH in protecting pregnancies and provide evidence against the involvement of thrombotic processes in thrombophilia-associated placental failure. Importantly, thrombin-mediated maternal platelet activation remains central in the mechanism of placental failure.

Placental fetal vascular thrombosis lesions and maternal thrombophilia

AIMS

Following intrauterine fetal death (IUFD), the placental fetal vessels undergo regressive changes. These changes are virtually indistinguishable from lesions that are the result of fetal vascular thrombosis (FVT). This study investigated the relation between these lesions and maternal thrombophilia.

METHODS

Placenta slides of 65 IUFDs with known maternal thrombophilia test results (compound MTHFR C677T and A1298C heterozygosity, n = 10; MTHFR 677TT homozygosity, n = 3; protein S deficiency, n = 0; factor V Leiden mutation, n = 2; prothrombin gene mutation G20210A, n = 1; lupus anticoagulant, n = 2; antiphospholipid syndrome, n = 1; MTHFR C677T heterozygosity, n = 5; MTHFR A1298C heterozygosity, n = 4; and MTHFR 1298CC homozygosity, n = 2) and of 30 livebirths with positive maternal thrombophilia test results (n = 5, 2, 0, 9, 2, 0, 2, 7, 2 and 1, respectively, for those thrombophilias) were microscopically examined for septation, fetal vessel thrombosis, intimal fibrin cushions, avascular villi, haemorrhagic endovasculitis and fibromuscular sclerosis.

RESULTS

Thirty of the 65 IUFDs had a positive maternal thrombophilia test; 22 of these 30 had FVT lesions. Thirty two of the 35 IUFDs with a negative maternal thrombophilia test had FVT lesions. Septation, defined as multiple lumens or 'recanalisation' in a placental vessel, was the lesion seen most often in IUFD (n = 41) whether by itself (n = 13) or in combination with other FVT lesions. Five of the 30 livebirths had FVT lesions but septation was not seen in any of the placentas from the 30 livebirths. FVT lesions did not have a significant relation with maternal thrombophilia.

CONCLUSIONS

The finding of fetal vascular thrombosis lesions in stillbirths does not imply thrombophilia as the cause of the fetal death. Factors other than thrombophilia may play a role in the cause of FVT lesions.

Placental histopathologic features in patients with thrombophilic mutations

The purpose of this article is to review the histopathologic findings in the placenta of women with a known thrombophilic mutation. The findings range from normal to severe pathologic features including decidual vasculopathy, placental infarctions, syncytial knotting, maternal floor infarction, fetal thrombotic vasculopathy, vasculitis, and chronic villitis. They are, however, not pathognomonic of thrombophilic states, nor are necessarily markers of perinatal damage. The prospective evaluation of cases with known thrombophilic mutations and the application of tissue microarray examination of the placenta may allow identification of major histopathologic features and molecular parameters associated with maternal and/or fetal thrombophilic states. This may assist clinicians in their consultation with patients and optimize management in future pregnancies.