Morphology of vitrified/warmed day-5 embryos predicts rates of implantation, pregnancy and live birth.

Although some post-thaw morphological predictors of pregnancy have been investigated in slow freezing of blastocysts, no such data have been published for vitrified and warmed blastocysts. Therefore, a prospective four-part score was applied to vitrified/warmed day-5 embryos to evaluate whether certain morphological parameters could serve as predictors of implantation, pregnancy and live birth. All morulae/blastocysts that were considered to be viable after warming were scored according to a previously unpublished grading system based on re-expansion, hatching (out of an artificial gap in the zona pellucida), extensive cytoplasmic granulation and presence of necrotic foci. Overall, 74% (202/273) of the vitrified concepti were found to be viable after warming. Early blastocysts showed better survival versus extended/hatching blastocysts (P < 0.01). Of the morphological parameters analysed, immediate re-expansion (P < 0.05) and hatching (P < 0.001) were positive predictors of the rates of implantation, pregnancy and live birth. The opposite holds for extensive cytoplasmic granulation (P < 0.05), which was negatively related. Accurate scoring of warmed blastocysts (within the first 2 h) allows for prediction of pregnancy outcome, and thus will help to further reduce the number of transferred embryos.