Correlation between embryological factors and pregnancy rate: development of an embryo score in a cryopreservation programme.

Purpose: To establish which embryo parameters, in frozen thawed embryo transfers, have the highest prognosis value in the establishment of pregnancy. The relative importance of different embryo parameters is used to develop an embryo score.

Methods: Retrospective analysis of the implantation rate in 356 frozen/thawed single embryo transfers. A logistic regression model is used to establish an embryo score.

Results: A direct correlation is established between the implantation rate and fresh embryo development (number of blastomeres and their symmetry), survival rate after thawing and mitosis resumption after overnight culture.

Conclusions: An embryo score is developed to determine the implantation potential of frozen/thawed embryos.