[Heparin therapy in pregnant women]

The prescription of heparin during pregnancy is an uncommon situation but a difficult one to manage because there are no reported therapeutic trials. The main indications are thromboembolic disease, valvular or congenital heart disease, cardiac arrhythmias and patients at high risk of thrombosis with blood clotting disorders. Non-fractionated heparin is the commonest form of anticoagulation in these circumstances as it does not cross the placental barrier; there are no teratogenic or haemorrhagic risks to the foetus. However, its dosage is difficult in pregnant women and this may lead to complications such as haemorrhage, heparin-induced thrombocytopaenia and osteoporosis; in addition, the duration of the treatment is often long and it can affect tolerance. Low molecular weight heparins are a promising alternative because of their long half-lives which give a more predictable dose-effect and reduce the number of daily injections. The risk of heparin-induced thrombocytopaenia is lower. At present, their legal prescription is limited to enoxaparin during the 2nd and 3rd terms of pregnancy as prophylactic treatment. The recommendations described in this article are the result of the 6th Consensus of the ACCP on antithrombotic treatment, which cautions the use of low molecular weight heparin during pregnancy. Different therapeutic regimes are presented according to the degree of thromboembolic risk. In patients with mechanical valvular prostheses, the recommendations are variable, with many workers, especially European groups, preferring anticoagulation to heparin from the 12th to the 36th week of pregnancy because of the greater efficacy of this particular indication. Peridural anaesthesia may be carried out with heparin therapy providing the level of anticoagulation is monitored and the procedure is performed under well controlled conditions. In cases presenting formal contra-indications to heparin therapy, heparinoids may be used instead. In future, low molecular weight heparin therapy will probably play a larger role in anticoagulation during pregnancy and in all the potential therapeutic indications.