THE IMPACT OF POST-THAW BLASTOCELE EXPANSION GRADE PROGRESSION ON ONGOING PREGNANCY RATES IN FROZEN-THAWED BLASTOCYST TRANSFER CYCLES

Objective

This study aims to examine the impact of the degree of progression in blastocele expansion grade from pre-vitrification to post-thaw stages on ongoing pregnancy rates (OPRs) in frozen-thawed blastocyst transfer cycles.

Materials and Methods

This retrospective cohort study was conducted at Hacettepe University, IVF Unit, between January 2014 and June 2024. The study included patients aged 20-44 years, with a BMI ≤ 35, who underwent single blastocyst embryo transfer with no preimplantation genetic tests or a partner with azoospermia. Embryos were initially graded at the pre-vitrification stage using the Gardner grading system. After thawing, they were re-evaluated 4-6 hours later to assess changes in the degree of blastocyst cavity expansion. Embryos were categorized into No progression, +1 progression (progression by one stage), and +2 progression (progression by two stages) groups. Data analysis included adjustments for BMI, maternal age, FET protocol type, and cycle number. The primary outcome, ongoing pregnancy, was defined as the presence of an intrauterine fetal heartbeat.

Results

The study included 449 single blastocyst transfer cycle. The OPRs for each combination of blastocyst morphological grade and blastocele expansion grade progression groups, and the odds ratios (OR) of OPRs compared to the reference group (poor embryo transfer with no progression of expansion) are presented in the Table 1. Univariately, both blastocyst morphology (excellent, good, average, and poor grading) and the degree of progression in blastocele expansion grade (0, +1, and +2 grading) have moderate accuracy in predicting pregnancy outcomes, with AUC values of 0.621 [0.574-0.667] and 0.630 [0.584-0.677], respectively. However, the DeLong test results show no statistically significant difference between the two AUC values (p = 0.617).

Discussion and Conclusion

These findings suggest that blastocysts with an advancement in blastocele expansion grade compared to their pre-vitrification evaluation have higher OPRs than those with no advancement. The results indicate that embryological evaluation at the post-thaw stage could be a predictive factor for OPRs.