EFFECT OF POST-THAW CHANGE IN EMBRYO SCORE ON SINGLE EUPLOID EMBRYO TRANSFER SUCCESS RATES.

OBJECTIVE: To assess whether the change in embryo morphology from pre-cryopreservation to post-thaw is associated with embryo transfer success rates in single euploid embryo transfer cycles.

DESIGN: Retrospective cohort study SUBJECTS: Patients who underwent a single euploid embryo transfer cycle from September 2016 - April 2022 were included. A decision support tool was used to assign each embryo a reproductive potential score based on the day of biopsy, expansion, and grade of trophectoderm and inner cell mass (ICM) at the time of cryopreservation and post-thaw.(1) Embryos were divided into 4 groups: Group 1 included embryos with the same score post-thaw (reference), Group 2 higher score, Group 3 lower score, and Group 4 embryos that did not re-expand post-thaw.

INTERVENTION(S): No interventions administered.

MAIN OUTCOME MEASURES: Primary outcome was live birth rates per embryo transfer (LBR). Secondary outcomes included chemical pregnancy, clinical pregnancy, and clinical pregnancy loss rate. Comparative statistics and univariate analyses were performed using Kruskal-Wallis and chi-square tests. Multivariate logistic regression fitted with generalized estimating equation was performed to compare the odds of live birth between groups.

RESULTS: A total of 7750 embryo transfers performed for 4613 patients met inclusion criteria: 5331 in Group 1, 486 in Group 2, 1726 in Group 3, and 207 in group 4. On univariate analysis, there was a statistically significant difference in LBR between groups 1, 2, 3, and 4 (55.8% vs 51.4%, 47.5%, 26.6%, p<0.0001). Logistic regression controlling for oocyte age, AMH, BMI, endometrial thickness, year of embryo transfer, time from thaw to final grading, and embryo score prior to cryopreservation showed significantly lower odds of LBR when the embryo was downgraded (OR 0.70, CI 0.62-0.79, p=<.0001) or did not re-expand (OR 0.36, CI 0.26-0.51 p=<.0001) compared with no change in score. When controlling for all variables, there was a significant increase in odds of live birth between embryos that had higher score post-thaw versus those without a change (OR 1.42, CI 1.14-1.76, p=0.002). There was no significant difference in clinical pregnancy loss rate among the 4 groups.

CONCLUSIONS: The change in quality of the embryo post-thaw is an important factor in embryo transfer success. In an adjusted analysis, the chemical pregnancy, clinical pregnancy, and LBR per embryo transfer are all significantly decreased in embryos that were downgraded or did not expand on the day of single euploid embryo transfer. Embryos that re-expand and improve their quality post-thaw have the highest odds of live birth.