For women with recurrent miscarriage and high blood clotting, heparin sodium can be used during pregnancy to protect the fetus. The role of Danaheparin in fetal protection includes the following aspects: first, it can improve blood coagulation, reduce blood viscosity, and has anticoagulation effect, which can improve the blood supply of pregnancy sac implantation and placenta, and avoid various complications caused by placenta shallow implantation. Second, it has immunomodulatory effect and inhibits the immune response produced by antiphospholipid antibody. Third, it promotes the proliferation, invasion and differentiation of trophoblast cells, inhibits trophoblast apoptosis, protects vascular endothelium and promotes the growth of placenta.