studying of efficiency low-molecular heparin for preventive maintenance and treatment of thromboembolic disorders in pregnant women, carriers of F-V- L and F-II-20210 G-A mutation. Under supervision, there were 27 women with thrombosis during pregnancy from 19 to 39 years old. The lower extremities veins thromboses was diagnosed by duplex sonography. F-V- Leiden, F-II-20210 G-A and MTHFR C 677T gene mutation was defined by PCR-PELP method. To all pregnant women Fraxiparin and vitamins of B group was appointed during pregnancy period; at presence of MTHFR a folic acid was appointed in addition. It is concluded that application of Fraxiparin is an effective method of treatment of thrombosis during pregnancy and women--carriers F-V- Leiden, F-II-20210 G-A and MTHFR C 677T gene mutation. High efficiency of Fraxiparin confirms with change of parameters of various parts of a hemostasis and return development of thrombosis evidence.