Low molecular weight heparins: a guide to their optimum use in pregnancy.

The incidence of pulmonary embolism (PE) and venous thromboembolism (VTE) is higher in pregnant patients than in non-pregnant patients. The incidence of thrombosis in all pregnancies is reported to be between 0.05 and 1%, and an incidence as high as 3% may be present in women after caesarean section. Anticoagulant medication is prescribed during pregnancy in patients presenting with VTE, thrombophilia abnormalities, or a history of PE or VTE. Since unfractionated heparin (UH) does not cross the placental barrier, it has become the gold standard anticoagulant therapy during pregnancy. Oral anticoagulants may also be prescribed during the second trimester but they cross the placental barrier. Low molecular weight heparins (LMWH) are effective, easy to use and have good safety profiles. The practical conditions of use have yet to be validated for pregnancy settings. In the absence of an approved indication, LMWH use during pregnancy is therefore the responsibility of the practitioner. However, several studies on LMWH as prophylaxis for PE or VTE have shown that such products are effective with good safety. Moreover, LMWH use is associated with reduced frequencies of thrombocytopenia and osteoporosis compared with UH use. Very few studies on LMWH use for the treatment of PE or VTE during pregnancy have been published, but the safety of LMWH use in this setting appears to be good. The review of the use of LMWH in pregnancy settings includes recommendations on the practical conditions of use. In the absence of large-scale, randomised, double-blind trials in such settings (which are needed), we propose the use of LMWH as prophylaxis for PE and VTE during pregnancy, but not for the treatment of these conditions. In prophylaxis settings, dalteparin sodium and enoxaparin sodium have been the most widely studied LMWH and we believe that priority should therefore be given to those products. Pending approval of LMWH for use in pregnancy, the use of LMWH off-label is the practitioner's responsibility.