2024-11-0920191464-727310.1080/14647273.2018.14680912-s2.0-85046401103http://dx.doi.org/10.1080/14647273.2018.1468091https://hdl.handle.net/20.500.14288/9809The goal of this retrospective cohort study was to compare survival, implantation, clinical and ongoing pregnancy rates between blastocysts that were vitrified on post-fertilization days 5, 6 and 7. Before vitrification, blastocysts were evaluated in terms of morphology and blastocyst expansion, inner cell mass and trophectoderm quality. They were thawed and transfered in a subsequent artificial cycle. Embryo implantation rates were 39%, 25% and 25% for blastocysts that were vitrified on days 5, 6, and 7, respectively (p = 0.006). Clinical and ongoing pregnancy rates were 19%, 12%, 13% (p = 0.100) and 9%, 7%, 12% (p = 0.99) for days 5, 6 and 7 blastocysts, respectively. Day 5 blastocysts had significantly higher full-collapsing score after assisted-hatching compared to days 6 and 7 blastocysts (p = 0.014). As blastocyst quality increased, implantation and clinical pregnancy rates increased in all groups and both parameters were statistically significantly higher on day 5 blastocysts than on days 6 or 7 (p = 0.001). It was clearly found that good quality blastocysts obtained on day 5 have higher implantation and clinical pregnancy rates than 6th and 7th day cryopreserved embryos. There were no statistically significant differences between the cryopreserved embryos on days 6 and 7 regarding the implantation, clinic and ongoing pregnancy rates.ObstetricsGynecologyReproductive biologyJournal Article1742-814947701240000911136