Heparin has also been used in conjunction with aspirin to prevent blood clotting. The rational for using heparin is that it is a blood thinner and inhibits clot formation by a different pathway that the aspirin. While the effectiveness of heparin and aspirin for treatment of women with elevated circulating antiphospholipid antibodies and a history of recurrent miscarriage is well accepted, the use of heparin with or without aspirin to enhance implantation rates has been controversial. Most clinical trials of women with elevated antiphospholipid antibodies and a history of implantation failure undergoing IVF/ET show no enhancement of implantation rates with heparin and aspirin compared with no treatment. This observation is not surprising since the action of heparin is on the cells lining the blood vessels and pre- and peri- implantation pregnancy loss occurs before placental blood vessels appear. The combination of both heparin and aspirin given to women experiencing repeat pregnancy loss who had antiphospholipid antibodies are associated with a live birth rate of 80% compared with a live birth rate of 44% in women receiving aspirin alone. Live birth rates with heparin, aspirin and a steroid called prednisone are 74%. Thus no enhancement of live birth rates are noticed when prednisone is added to heparin and aspirin therapy for treatment of recurrent miscarriage.
Heparin is usually administered at a dose of 5,000-10,000 units subcutaneous twice a day along with aspirin 80mg each day. In women with a circulating lupus-like anticoagulant, more heparin may be required. The side effects of heparin therapy include bleeding, decreased platelet count and osteoporosis or thinning of the bones. Calcium supplementation (two tablets of Tums a day) is recommended while taking heparin. Low molecular weight heparins such as Lovenox and Fragmin have also been used to treat recurrent pregnancy loss associated with thrombophilias, either acquired or inherited.