Authors: Savage N., Bopp, B., Will, M., Anspach-Will, E., O’Leary, K., Adaniya, G.
Objective: To determine if the day of blastulation (DoB) could be used as a biomarker of embryo success.
Design: Retrospective study in a private assisted reproductive technology practice.
Materials and Methods: Cycle data was collected from 297 frozen embryo transfer (FET) cycles between January 2020 to December 2021 that contained blastocysts frozen without genetic testing either on day 5 (N = 209) or day 6 (N = 88) of embryogenesis. The primary goal was to compare the rates of positive β-hCG level (≥20 mIU/ml), presence of a gestational sac (SAC), and fetal cardiac activity (FCA) between the different days of blastulation. Secondary outcomes reviewed the effects of degree of expansion (DoE), graded morphology of the inner cell mass (ICM), and graded morphology of the trophectoderm(TE-m). Statistical analysis between DoB utilized a two proportions Z test with an p≤0.05 considered significant for all subgroups.
Results: Rates of positive β-hCG with day 5 embryos was significantly higher than with day 6 embryos (70% vs. 52%, p=0.003). There was a significant difference between day 5 and day 6-derived embryos when comparing SAC rates (63% vs. 47%, p=0.015) and FCA rates (58% vs. 42%, p=0.02), respectively. Further analysis revealed a significant difference between hatching blastocysts transferred on day 5 and day 6 in terms of β-hCG level (p=0.009), SAC (p=0.01), and FCA (p=0.02). However, there was no significant difference between the day 5 and day 6 cohorts in terms of the early blastocysts and expanded blastocysts groups. Additional evaluation of ICM showed no significant difference between the two cohorts, regardless of morphological grade. A trend was observed between day 5 and day 6 embryos in the morphological subgroup of A-graded trophectoderm in terms of β-hCG level (p=0.06), but not for SAC or FCA rates. No other significant differences or trends in the trophectoderm quality subgroups were seen.
Conclusions: DoB is a significant biomarker of embryo success. Subgroups that examine DoE versus DoB show a significant difference when looking at hatching blastocysts, but not the earlier expansion stages. This could be due to the thinning zona in combination with the degree of growth in hatching blastocysts, but further research is required to elaborate on the difference.