摘要Objective: To elucidate the possible role of unfractionated heparin in patients with failed repeated in in vitro fertilization and embryo transfer (IVF-ET) and thrombophilia. Methods: This case control study evaluated the efficacy of the unfractionated heparin in increasing the pregnancy and implantation ratio in women with recurrent IVF-ET failures. Eighty-six women received in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) with a record of three or more previous IVF-ET failures. Participants were randomly distributed into two groups. Group A (n=43) received unfractionated heparin 5000 IU twice daily, and group B (n=43) did not take any antithrombotic drugs. Coagulation abnormalities such as factorⅤ Leiden (FVL) mutation, methylene tetra hydro folate reductase (MTHFR) mutation and prothrombin mutation (F栻) were evaluated. Age, body mass index, basal follicular stimulating hormone, basal estradiol, duration of infertility, and number of IVF-ET failures were compared between two groups. Results: 45.0％ and 17.4％ of women were pregnant with and without MTHFR and prothrombin mutation, respectively, when they received unfractionated heparin treatment. The implantation rate was more in group A (12.5％) than group B (4.3％) and differences in the fertilization rate of the two groups were observed (27.7％ vs. 35.9％). The clinical pregnancy rate per cycle was remarkably more in group A (30.2％) than group B (14.0％). Conclusions: Heparin is a safe and valuable treatment for patients with repeated IVF-ET failures. The clinical pregnancy and implantation rates are higher in the heparin-treated group in contrast with the control group.