Low Molecular Weight Heparin to Improve Pregnancy Outcome in Patients With Recurrent Implantation Failure

Inclusion Criteria: * History of three or more consecutively failed In Vitro Fertilization (IVF) cycles after embryo transfer. * Normal uterine cavity (as assessed by hysteroscopy or HSG). * Normal hormonal investigation: TSH, PRL, FBS. * Normal acquired/inherited thrombophilia profile: LAC, ACA IgG/IgM, Prot S, Antithrombin III, beta-2 glycoprotein, Factors V, II, MTHFR. * Normal semen analysis and mild/moderate male factor (Total motile sperm count \> 5 million/ml and/or normal WHO morphology \>20%. * Patient provides written informed consent. Exclusion Criteria: * Evidence of low ovarian reserve by at least one of the following: AMH ≤ 1,5 ng/mL and/or basal CD 3 FSH ≥ 10 mIU/mL and/or basal CD 3 Estradiol ≥ 60 ng/mL and/or previous egg collection yield ≤ 3 oocytes. * Preexisting medical condition (thyroid disease, diabetes mellitus, hypertension, pulmonary conditions, cardiac condition…). * Severe male factor infertility (Total motile sperm count \< 5 million/ml and/or normal WHO morphology \<20%). * Hypersensitivity to Heparin or its derivatives. * Acquired thrombophilia. * Active hemorrhage or increased risk of bleeding due to impairment of homeostasis. * Severe impairment of liver or pancreatic function. * Severe renal insufficiency (Creatinine Clearance \< 30 ml/min). * Injuries to or operations on the central nervous system, eyes and ears within the last 2 months. * Disseminated Intravascular Coagulation (DIC) attributable to heparin-induced thrombocytopenia. * Acute bacterial endocarditis and endocarditis lenta. * Any organic lesion with high risk of bleeding (e.g.: active peptic ulcer, hemorrhagic stroke, cerebral aneurysm or cerebral neoplasms).