A study to determine if embryo cryopreservation influences the potential of rapidly growing embryos to successfully implant in uterine environments not influenced by controlled ovarian hyperstimulation.

PURPOSE: To determine if transferring at least one embryo with eight blastomeres at 72 hours improves prognosis of donor oocyte recipients. The study aim was to verify if cryopreservation increases or decreases the advantage of rapidly growing embryos. The study could exclude the influence of controlled ovarian hyperstimulation (COH) on the uterine environment. METHODS: All transfers, fresh or frozen, using exclusively embryos that resulted from fertilization of donor oocytes over a three-year period were evaluated. RESULTS: Significantly higher pregnancy rates (PRs) and delivery rates were found in donor oocyte recipients receiving at least one eight-cell embryo compared to transfers without any eight-cell embryos. These differences were not found when comparing frozen embryo transfers (ETs). The data could not be explained by confounding variables. CONCLUSIONS: The inclusion of at least one 8-cell embryo on day 3 fresh ET resulted in higher PRs even without the influence of COH. However, higher blastomere number did not influence frozen ET outcome.