Blastocoele expansion: an important parameter for predicting clinical success pregnancy after frozen-warmed...

To assess the predictive value of each individual morphological parameter: blastocoele expansion degree, inner cell mass (ICM), and trophectoderm (TE) grades on the clinical pregnancy outcome in frozen-warmed embryo transfer (FET) cycles.

This is a retrospective cohort study, including 1154 FET cycles receiving vitrified-warmed one or two blastocysts transfer from August 2011 through to May 2018. The correlation between blastocyst morphology parameters and clinical outcome after FET was assessed.

In the subgroup analysis based on clinical pregnancy, the patients who achieved clinical pregnancy had a significantly higher degree of blastocyst expansion (3.69 ± 0.68 vs. 3.53 ± 0.78, P = 0.000) and had a thicker endometrium (9.65 ± 1.63 vs. 9.28 ± 1.64) compared with those with non-clinical pregnancy. The logistic regression analysis showed that among the three blastocyst morphology parameters, only the blastocoele expansion degree was significantly correlated with the clinical pregnancy outcome and had ability to predict the outcome after FET cycles with one or two vitrified-warmed blastocysts transferred. Both ICM and TE stages were not associated with pregnancy outcomes.

The blastocoele expansion degree may be essential for successful pregnancy and should be given priority when selecting frozen blastocyst for transfer.