Beneficial effect of long zona dissection on frozen-thawed blastocysts at a young age.

To assess the appropriateness of assisted hatching using long zona dissection of human frozen-thawed blastocysts at the time of warming, especially in women over 35 years of age or with repeated implantation failures. Of 177 frozen-thawed blastocyst transfer cycles, 89 control cycles had an intact zona and 88 cycles had assisted hatching using long zona dissection of human thawed blastocyst at the time of warming. These two groups were further subdivided by age to a total of four subgroups: ≤34 years (assisted hatching,  = 39; controls,  = 39) and ≥35 years (assisted hatching,  = 49; controls,  = 50). Twenty-seven cycles in the control group and 28 cycles in the assisted-hatching group had repeated implantation failures. The clinical and ongoing pregnancy rates and the implantation rate between the two groups were analyzed retrospectively. The clinical pregnancy and implantation rates in women ≤34 years were significantly higher after the application of assisted hatching compared with the control group (87.2% and 71.2% 56.4% and 46.6%,  < 0.001). The clinical pregnancy and implantation rates of women with repeated implantation failures were higher after the application of assisted hatching compared with the control group (64.3% and 46.3% 48.1% and 34.1%), but this difference was not statistically significant. Routine assisted hatching using long zona dissection at the time of warming on frozen-thawed blastocysts is a safe and easy method to perform and is extremely beneficial for increasing the pregnancy rate in young women ≤34 years of age, but not in women ≥35 years of age. Despite increased pregnancy and implantation rates in patients with repeated implantation failures, statistical significance was not achieved. (Reprod Med Biol 2007; : 211-218).