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.