OBJECTIVE: The Thrombophilia gene mutations are described as cause of Recurrent Pregnancy Loss (RPL).In RPL Mexican patients, there aren't studies reporting Plasminogen Activator Inhibiting Factor(PAI-I) gene mutation prevalence, we just have information about Methylenetetrahydrofolate Reductase, which has a frequency of 47% in specific groups in Mexican population.The thrombophilia gene mutation induce placentary thrombosis, as a cause of miscarriage. We determine the frequency of these defects in a specific group of Mexican patients with RPL.DESIGN: Observational, retrospective and Descriptive.MATERIALS AND METHODS: 114 patients having RPL were included; from May 2003 to March 2008. Complete RPL work up was done, once it was reported as negative, a sample was taken by a buccal swabs smear and analyzed through the Polymerase Chain Reaction method in the Millenova Immunology Laboratory (Chicago IL, USA) and IMMUNOREP (México City) searching for the following Thrombophilia Genes mutations: V Leiden Factor (VLF) - Y1702C, H1299R and G1691A -, Methylenetetrahydrofolate Reductase gene (MTHFR) - C677T and A1298C -, Factor II Prothrombin (FII) - G20210A -, Factor XIII (FXIII) - V34L -, b-Fibrinogen (b-F) - 455 G>A -, - PAI-I 4G/5G - and a/bHuman Platelet Antigen (HPAI), after diagnosis was done, the antithrombotic treatment was given and couples looked for pregnancy.RESULTS: In 114 patients, with an age rank 26 to 42 years old, (SD±3.4),only 2/114 (1.7%) of them, were negative to any mutation, 112/114(98.3%) were positive to at least one of the mutations. 108/112 (96.4%) patients had 2 or more mutation. The most frequent mutation was PAI-I 4G/5G in 93/112 (83%) patients. The second most frequent mutation was the MTHFR C677T in 76/112 (67.8%) cases, and the less frequent mutation was V Leiden Factor, in 8/112 (7.1%) cases. From the 112 positives patients for someone of the mutations, only 63/114 (55.2%) underwent treatment to get pregnant, in this group, only 47/63 (74%) got pregnant, and at the end, we got 100% of healthy newborn.CONCLUSIONS: The prevalence of MTHFR gene mutations in Mexican RPL patients is higher than reported in worldwide literature; the PAI-I 4G-5G wasn't been studied in Mexican population, this mutation stop the conversion of Plasminogen to Plasmin, avoiding the clot dissolution, causing a hiperthrombotic state in the microcirculation, and maybe at placentary level, as a postulated cause of RPL in patients with the features we included. Our pregnancy rate is higher than reported in other similar studies. OBJECTIVE: The Thrombophilia gene mutations are described as cause of Recurrent Pregnancy Loss (RPL).In RPL Mexican patients, there aren't studies reporting Plasminogen Activator Inhibiting Factor(PAI-I) gene mutation prevalence, we just have information about Methylenetetrahydrofolate Reductase, which has a frequency of 47% in specific groups in Mexican population.The thrombophilia gene mutation induce placentary thrombosis, as a cause of miscarriage. We determine the frequency of these defects in a specific group of Mexican patients with RPL. DESIGN: Observational, retrospective and Descriptive. MATERIALS AND METHODS: 114 patients having RPL were included; from May 2003 to March 2008. Complete RPL work up was done, once it was reported as negative, a sample was taken by a buccal swabs smear and analyzed through the Polymerase Chain Reaction method in the Millenova Immunology Laboratory (Chicago IL, USA) and IMMUNOREP (México City) searching for the following Thrombophilia Genes mutations: V Leiden Factor (VLF) - Y1702C, H1299R and G1691A -, Methylenetetrahydrofolate Reductase gene (MTHFR) - C677T and A1298C -, Factor II Prothrombin (FII) - G20210A -, Factor XIII (FXIII) - V34L -, b-Fibrinogen (b-F) - 455 G>A -, - PAI-I 4G/5G - and a/bHuman Platelet Antigen (HPAI), after diagnosis was done, the antithrombotic treatment was given and couples looked for pregnancy. RESULTS: In 114 patients, with an age rank 26 to 42 years old, (SD±3.4),only 2/114 (1.7%) of them, were negative to any mutation, 112/114(98.3%) were positive to at least one of the mutations. 108/112 (96.4%) patients had 2 or more mutation. The most frequent mutation was PAI-I 4G/5G in 93/112 (83%) patients. The second most frequent mutation was the MTHFR C677T in 76/112 (67.8%) cases, and the less frequent mutation was V Leiden Factor, in 8/112 (7.1%) cases. From the 112 positives patients for someone of the mutations, only 63/114 (55.2%) underwent treatment to get pregnant, in this group, only 47/63 (74%) got pregnant, and at the end, we got 100% of healthy newborn. CONCLUSIONS: The prevalence of MTHFR gene mutations in Mexican RPL patients is higher than reported in worldwide literature; the PAI-I 4G-5G wasn't been studied in Mexican population, this mutation stop the conversion of Plasminogen to Plasmin, avoiding the clot dissolution, causing a hiperthrombotic state in the microcirculation, and maybe at placentary level, as a postulated cause of RPL in patients with the features we included. Our pregnancy rate is higher than reported in other similar studies.