Severe cytoplasmic abnormalities of the oocyte decrease cryosurvival and subsequent embryonic development of cryopreserved embryos.

ABSTRACT

BACKGROUND: Abnormalities of oocyte morphology affect embryo quality and viability. Whether morphological abnormalities of the oocyte influence cryosurvival and further development of derived embryos is not known. The aim of this study was to compare cryosurvival and progression to the blastocyst stage of frozen-thawed embryos derived from normal and abnormal oocytes. METHODS: A total of 5292 Grade 1 and 2 embryos from 964 women were frozen, thawed and subsequently cultured up to the blastocyst stage. The study was performed on excess embryos from patients who did not opt for cryopreservation. Cryosurvival, progression to the blastocyst stage and hatching were correlated with morphological characteristics of the oocytes that embryos were derived from. RESULTS: Presence of a cytoplasmic abnormality of the oocyte significantly decreased cryosurvival. This detrimental effect was more pronounced in embryos derived from oocytes with vacuolar cytoplasm or with central granulation. Furthermore, these embryos did not have the potential to develop into good quality blastocysts or reach the hatching stage. On the other hand, presence of a single extracytoplasmic abnormality of the oocyte did not affect cryosurvival and the potential to develop into good quality blastocysts. Grade 2 embryos derived from oocytes with irregular shape or a large perivitelline space had decreased cryosurvival. However when these embryos survived cryopreservation, their potential to develop good quality blastocysts or to reach hatching stage was unaffected. CONCLUSIONS: Embryos derived from oocytes with vacuolar cytoplasm or central granulation do not seem to bear the potential to develop good quality blastocysts or to reach hatching stage after cryopreservation. The presence of extracytoplasmic abnormalities alone does not affect blastocyst development despite decreasing cryosurvival.