Revisiting embryo selection: inner cell mass outweighs the trophectoderm in predicting live birth in single frozen...

To assess the value of individual blastocyst morphological parameters in predicting live birth in single frozen blastocyst transfers.

This was a retrospective cohort study in which total of 2694 single frozen blastocyst transfers, between Jan 2019 and Dec 2023, were analyzed. The primary outcome measure was live birth. Multivariate logistic regression analysis was used to study the independent effect of all three morphological parameters namely- expansion stage, inner cell mass (ICM) and trophectoderm (TE) grade as predictors of live birth in frozen embryo transfer cycles.

Expansion grade 5 i.e. hatching blastocysts, was associated with significantly higher chance of live birth compared to a grade 4 expanded blastocyst with an adjusted odds ratio [aOR] of 1.234 (95% CI 1.039-1.466; p = 0.017). The ICM also continued to be a significant predictor of live birth as embryos with grade B ICM were associated with a ∼ 27% reduction in odds (aOR = 0.727; 95% CI 0.574-0.920; p = 0.008), while grade C was observed to have the strongest impact, lowering the odds of live birth by ∼ 70% compared to grade A (aOR = 0.293; 95% CI 0.119-0.720; p = 0.007). In contrast, the impact of TE on live birth was found to be less significant (TE grade B versus A: aOR = 0.843; 95% CI 0.696-1.022; p = 0.083).

Our findings suggest that a day 5 hatching blastocyst with pre-freeze grade A ICM and grade A or B TE would be associated with the highest probability of live birth.