Objective To identify the factors influencing the success of frozen-thawed embryo transfers, whether originating directly from current cycles or from their matching fresh cycles. Methods Analysis of 273 frozen-thawed embryo transfer cycles and their matching fresh embryo transfer cycles, with respect to maternal, embryological and clinical factors, comparing successful to unsuccessful cycles. Results The cumulative clinical pregnancy and live birth rates following fresh ET and corresponding FETs were 50.5% and 38.8%, respectively. No outcome measure differed between fresh and frozen ET's. Only maternal age, number of oocytes retrieved and fertilized, and number of cleaved embryos in the fresh cycle were correlated with a higher pregnancy or live birth rate in the FET cycle. None of the other parameters had any effect on the outcome. Pre-freezing embryo quality and blastomere survival rate had no effect on pregnancy/live birth rates. Conclusion Clinical pregnancy and live birth rates of fresh and frozen ETs were not significantly different. The only parameters that affected FET success were those resulting from the patient's age and ovarian reserve at the time of oocyte aspiration. Post-thawing blastomere survival rate and type of endometrial preparation for FET did not affect the success rate.
