General considerations

There are no universally accepted protocols for the management of anticoagulation in pregnancy. There are few controlled studies and much of the information relates to non-pregnant subjects. Both oral anticoagulants and heparin have advantages and disadvantages in pregnancy. LMWH are a significant advance in management.

Warfarin crosses the placenta and is teratogenic in the first trimester. Exposure during weeks 6-12 can cause warfarin embryopathy with nasal hypoplasia, stippled epiphyses and other manifestations. Incidence ranges from <5% to 67% in reported series. Warfarin at any stage of pregnancy is associated with CNS abnormalities and increased risk of fetal haemorrhage in utero and at delivery.

Heparin (UFH and LMWH) does not cross the placenta and poses no teratogenic or haemorrhagic threat to the fetus. Maternal complications include haemorrhage (severe in <2%), thrombocytopenia (severe in <1%) and osteoporosis, usually asymptomatic and reversible but rare cause of vertebral fractures. LMWH may have fewer complications cf. unfraction-ated (UF) heparin.

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