duration of storage does not influence pregnancy outcome in cryopreserved human embryos

background:   objective: the aim of our study was to assess the effect of storage duration of frozen embryo on art outcome.   materials and methods: in this retrospective study the data of 651 frozen-thawed embryo transfer cycles were assessed over a 36-months period. our patients were categorized according to storage time of freeze. group i: less than 90 days, group ii: between 90-365 days. group iii: between 365-730 days. group iv: between 730-1095 days. group v: more than 1095 days. clinical pregnancy and implantation rate were defined and statistical analysis was performed using student t-test and chi-square. results: according to our finding patient’s mean age was 31.05±5.231 years (range, 18-53 years), and 1204 embryos were transferred .the mean storage duration was 296.72±301.82 days. the mean number of embryo transferred per cycle was similar between groups (p=0.224). according to our analysis clinical pregnancy rate per embryo transfer cycle was similar between groups (p=0.563). conclusion: our results showed that duration of storage had no negative effects on implantation of cryopreserved embryos. in our literature review we found a little article in this context. however our study showed duration of freezing don’t have any negative effects on implantation and pregnancy outcome, but more studies are needed to evaluate long term effects of storage duration on babies were born by cryopreserved embryos. cryopreservation of embryos has been an usual component of clinic in assisted reproductive technology (art) programs. recently the dramatic increase in cryobiology activity in the clinical centers has enhanced methods of freezing and improved vitrification protocols are being developed.