To investigate the predictors of postthaw blastomere survival and the relationship of blastomere survival to the outcome of frozenthawed embryo transfer (FET) cycles. Retrospective study. An IVF unit in a tertiary care facility. Infertile women undergoing FET cycles with embryos cryopreserved on day 3 postinsemination. FETcycles. Embryo survival postthaw, pregnancy (PR), clinical pregnancy, and implantation rates. A significant impact of postthaw blastomere survival on the outcome of FET cycles was noted. The thawed embryos in the low survival tertile resulted in significantly impaired implantation rate, clinical pregnancy rate, and PR compared to embryos in the high survival tertile. An inverse association was noted between serum P levels on the day of hCG administration and postthaw blastomere survival. We have demonstrated that postthaw blastomere survival is predictive of success of FETcycles. The relationship of poor postthaw embryo survival in the setting of elevated P is novel and not hitherto described. To investigate the predictors of postthaw blastomere survival and the relationship of blastomere survival to the outcome of frozenthawed embryo transfer (FET) cycles. Retrospective study. An IVF unit in a tertiary care facility. Infertile women undergoing FET cycles with embryos cryopreserved on day 3 postinsemination. FETcycles. Embryo survival postthaw, pregnancy (PR), clinical pregnancy, and implantation rates. A significant impact of postthamblastomere survival on the outcome of FET cycles was noted. The thawed embryos in the low survival tertile resulted in significant impaired implantation rate, clinical pregnancy rate, and PR compared to embryos in the high survival tertile. An an association was noted between serum P levels on the day of hCG administration and postthaw blastomere survival. We have demonstrated that postthamblastomere survival is predictive of success of FETcycles The relationship of poor postthaw embryo survival in the setting of elevated P is nove l and not hitherto described.