Prediction of live birth in frozen-thawed single blastocyst transfer cycles by pre-freeze and post-thaw morphology

Abstract

Study question: What pre-freeze and post-thaw morphological parameters can be used to predict live birth outcomes after frozen-thawed blastocyst transfer cycles?

Summary answer: Pre-freeze blastocoele expansion and trophectoderm (TE) grade and post-thaw degree of re-expansion are the most significant predictors of live birth in frozen-thawed blastocyst transfer cycles.

What is known already: Currently, blastocoele re-expansion after thawing is used to indicate blastocyst cryosurvival and reproductive potential. The predictive roles of other pre-freeze and post-thaw morphological parameters are neglected.

Study design, size, duration: This was a retrospective study of all the patients who received a frozen-thawed single blastocyst transfer (n = 1089) at our clinic between March 2008 and October 2011.

Participants/materials, setting, methods: Pre-freeze morphological parameters analyzed for all blastocysts included grade of blastocoele expansion, inner cell mass and TE. A group of blastocysts (n = 243) were also graded for post-thaw parameters: degree of blastocoele re-expansion, viability and cell contour. Univariate and multivariate generalized estimating equations (GEEs) models were used to identify the confounders that statistically significantly affected live birth outcomes and to investigate the independent effect of significant pre-freeze and post-thaw morphological parameters. Stepwise logistic regression analysis was used to select the best independent morphological predictors of live birth. Pearson correlations and linear regression analyses were performed to determine the relationship between morphological parameters and possible covariates.

Main results and the role of chance: Multivariate GEE models estimated that the odds of live birth increased by ∼36% for each grade of expansion (P = 0.0061) and decreased by 29% for blastocysts with grade B TE compared with grade A TE (P = 0.0099). Furthermore, the odds of live birth increased by ∼39% (P = 0.0042) for each 10% increase in degree of re-expansion. Blastocoele expansion and TE grade were selected as the most significant pre-freeze morphological predictors of live birth and degree of re-expansion was selected as the best post-thaw parameter for prediction of live birth.

Limitations, reasons for caution: Blastocysts with poorer grades of morphology were not cryopreserved or transferred, limiting the ability to generalize our findings for grades of morphology not included in this study.

Wider implications of the findings: Blastocysts with higher pre-freeze grades of expansion and TE, irrespective of day of cryopreservation, should be given priority when thawing. Subsequently, re-expanding blastocysts, assessed within 2-4 h, with >60% viability should be transferred.

Study funding/competing interest(s): No external funding was obtained for this study. There was no competing interest.

Trial registration number: not applicable.