Growth retardation in human blastocysts increases the incidence of abnormal spindles and decreases implantation potential after vitrification.

STUDY QUESTION Does the human embryo growth rate affect the outcome of vitrified-warmed blastocyst transfer? SUMMARY ANSWER Following vitrification, the incidence of abnormal spindle morphology was increased and the implantation competence was decreased in growth-retarded embryos compared with normally developing embryos. WHAT IS KNOWN ALREADY Various types of spindle abnormality occur in human cleavage- and blastocyst-stage embryos. However, the incidence of abnormal spindle morphology in growth-retarded blastocysts is not known. Furthermore, there is conflicting data about the implantation potential of such blastocysts. STUDY DESIGN, SIZE, DURATION This was a retrospective cohort study including 878 single vitrified-warmed blastocyst transfers between 9 January 2010 and 10 July 2012, and an experimental study using 121 vitrified-warmed blastocysts donated to research. A comparison on the implantation potential and spindle shape of vitrified-warmed blastocysts was made between normally developing and growth-retarded blastocysts. PARTICIPANTS/MATERIALS, SETTING, METHODS In the clinical study, we compared the implantation rates of vitrified-warmed embryos that developed to the blastocyst stage on Day 5 after insemination (normally developing embryos) with those that required culture to Day 6 (growth-retarded embryo). In the experimental study, donated vitrified-warmed blastocysts were immunostained with an anti-α-tubulin antibody to visualize microtubules, an anti-γ-tubulin antibody to image centrosomes and Hoechst 33342 or 4,6-diamidino-2-phenylindole to visualize DNA. Confocal image analysis captured a z-series stack of 0.5-µm-thick optical sections encompassing the entire blastocyst. Only spindles with fusiform poles and with chromosomes aligned at the equator were classified as normal. MAIN RESULTS AND THE ROLE OF CHANCE The implantation rate of growth-retarded embryos (47%, n = 270) was significantly lower (P < 0.05) than that of normally developing embryos (57%, n = 608). A total of 533 spindles were analyzed in Day 5 and 6 vitrified-warmed blastocysts. The incidence of abnormal spindles in the growth-retarded embryos (47%, n = 274) was significantly higher (P < 0.01) than in the normally developing embryos (30%, n = 259). LIMITATIONS, REASONS FOR CAUTION Further studies are required to clarify the link between an increase in abnormal spindle formation and a decrease in embryonic implantation potential. WIDER IMPLICATIONS OF THE FINDINGS This study provided new insights into the possible implications of abnormalities in spindle formation in growth-retarded human blastocysts.