Pregnant women are more susceptible than non-pregnant women to forming blood clots in their veins (venous thrombosis). When these clots occur in the deep leg veins, the clot can break up and fragments (emboli) move to the lungs where they may block the blood flow to the lungs (pulmonary embolism). This can have serious consequences. Anticoagulants are used to treat clots and are given to pregnant women with increased susceptibility to clotting. These medications thin the blood to reduce the risk of the further thrombosis and reduce the risk of pulmonary embolism. An important complication of treatment is haemorrhage. During pregnancy heparin is the most common anticoagulant used, either the older unfractionated heparin (UFH) or the newer low molecular weight heparin (LMWH). Neither of these cross the placenta, and both have been shown to be safe during pregnancy, whereas there are concerns that warfarin may affect the fetus. LMWH has been shown to be more effective than UFH outside pregnancy.
In this review we planned to compare these two types of heparin in pregnancy for their ability to reduce clotting and their safety. We could not find any randomised controlled trials for inclusion in the review.
This means that we do not have any evidence from randomised controlled trials on the effectiveness of anticoagulation for deep vein thrombosis in pregnancy, and the effectiveness of LMWH compared to UFH. There is a need for further studies in this area.