Authors: Carrie Bedient, Kajal Verma, Ankita Raman, Leah Kaye, Mark Adamowicz, Martha Aguirre, Forest Garner, Bruce Shapiro

Materials and Methods:

Following conventional ovarian stimulation, oocyte retrieval, and insemination by intracytoplasmic sperm injection, embryos were cultured to the blastocyst stage. Prior to vitrification, the blastocysts were objectively measured. In subsequent thaw cycles, blastocysts were allowed at least two hours to re-expand before they were measured. Ongoing pregnancies were those with fetal cardiac activity at 10 weeks gestation. Linear regression analysis was used to assess the relationship between pre-freeze measurements (cross-sectional area of the inner cell mass [ICM area] expressed in square microns, and trophectoderm cell count assessed in an equatorial plane of focus) and post-thaw measurements of the same parameters. A P-value <0.05 was considered significant. R-squared values less than 0.25 were considered weak correlation.

Results:

A total of 358 single-blastocyst transfers were available for this study, in which 93.4% of thawed blastocysts were assessed as surviving, and 213 transfers resulted in ongoing pregnancy at 10 weeks (59.5%). Linear regression of post-thaw vs. pre-vitrification ICM area found a statistically significant correlation (P<0.0001), however, the strength of this relationship was weak (R-squared = 0.077). Linear regression of post-thaw vs. pre-vitrification trophectoderm cell count also found a statistically significant correlation (P<0.0001), but again, the strength of the relationship was weak (R-squared = 0.237). In cycles using PGT-A, the significant predictor of ongoing pregnancy in logistic regression was post-thaw ICM area (P=0.0124, R-squared = 0.033). In cycles without PGT-A, none of the available measures was a significant predictor of ongoing pregnancy.

Conclusions:

Pre-vitrification blastocyst morphometry is a weak predictor of post-thaw morphometry and outcome of thawed and transferred single blastocysts. Pre-vitrification measurements of the ICM and trophectoderm explained only small proportions (7.7% and 23.7%, respectively) of the variance of post-thaw measurements, and were not significantly correlated with ongoing pregnancy after transfer.

Impact:

Methods for selecting the first blastocyst to thaw and transfer are not yet well developed. Further research is needed to optimize such selection, in order to reduce the number of transfers needed to achieve pregnancy.