Abstract
PurposeApart from freezing/thawing related cryodamage, several additional factors have been identified as major players in the reduction of success rates after frozen embryo transfers. The post-thaw culture is particularly relevant as it may amplify environmental influences over a stressed embryo. In the present study the influence of the post-thaw culture duration on the implantation and developmental potential of cleavage stage embryos was evaluated.MethodsIn this retrospective evaluation, that spanned an 8-year period, 631 frozen-thawed embryos were allocated to one of two study groups, depending on their post-thaw culture period: 1) the long (18–24 h), or 2) the short (2–5 h) culture group. Groups were compared regarding implantation rate and live birth rate per embryo transferred. This comparison was corrected for the most common confounding factors such as maternal age at oocyte pick-up, number of transferred embryos, developmental day at freezing, blastomere survival after thawing, catheter used for transfer and year of procedure.ResultsImplantation and live birth rate per embryo transferred were inversely related to the duration of the post-thaw culture, as diminishing this period significantly increased both rates. Moreover, no advantage could be found for a long post-thaw culture period, even for embryos with observed mitotic activity.ConclusionThis retrospective analysis indicates that a short post-thaw culture period is associated with higher implantation and live birth rates per embryo. This study supports selection of frozen-thawed embryos strictly based on blastomere cryosurvival and raises the hypothesis that environmental factors may have an important role on embryo implantation and developmental potential during post-thaw culture.
Highlights
The two most common procedures to select embryos for frozen embryo transfer (FET) differ in the duration of the post-thaw culture: one relies upon the observation of blastomere proliferation, requiring a longer culture, generally overnight; the other relies upon the observation of blastomere survival after thawing, requiring a shorter culture
This study supports selection of frozen-thawed embryos strictly based on blastomere cryosurvival and raises the hypothesis that environmental factors may have an important role on embryo implantation and developmental potential during post-thaw culture
In order to account for their influence on the results, all analyses were adjusted for mean maternal age at ovarian pick-up (OPU), number of transferred embryos, developmental day at freezing, catheter used for transfer and year of procedure
Summary
The two most common procedures to select embryos for frozen embryo transfer (FET) differ in the duration of the post-thaw culture: one relies upon the observation of blastomere proliferation, requiring a longer culture, generally overnight; the other relies upon the observation of blastomere survival after thawing, requiring a shorter culture. FET is generally considered a well established technique, a large number of studies concentrate on the reasons for its lower success rate when compared to fresh embryo transfers [1, 2] Major contributors to such divergence have been extensively discussed and, as an attempt to elevate frozen embryo transfer (FET) outcome, the postthaw assessment of mitotic resumption became a widely employed strategy for embryo grading and selection [5, 6, 14, 18, 20, 22]. After an internal evaluation of our FET program, a tendency towards a better outcome following transfer of embryos thawed on the same day as transfer was identified In light of such observation, thawing began to preferentially be performed on the same day as transfer and embryo post-thaw selection based on mitotic activity was no longer a priority
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