P-553 Embryo collection improves clinical pregnancy outcomes in next-generation sequencing(NGS)-based preimplantation genetic testing for aneuploidy (PGT-A) euploid embryo transfers
Authors: Kim Y  I , Choi J  Y , Han S  J , Kim J  H , Yu E  J , Hur Y  J , Kim M  J , Park E  A , Kang K  Y , Lee H  C , Kim H  O , Kim Y  S , Yoon T  K 
Published: July 2024

Abstract

Study question
Is there still a significant impact of embryo-related characteristics on pregnancy rates in NGS based PGT-A euploid embryo transfers for advanced-age patients?

Summary answer
In single frozen euploid embryo transfers, priority of embryo transfer and grade significantly influence clinical pregnancy rates in women over 35 years old with PGT-A.

What is known already
It is widely recognized that better embryo grades and a shorter duration of blastulation are associated with favorable reproductive outcomes. Recent meta-analyses have affirmed these findings even in the context of transfer with euploid embryos. However, the impact of prioritizing the highest-ranked embryo among multiple vitrified euploid embryos on pregnancy rates remains unclear. The lack of research in this area implies a gap in understanding whether selecting embryos for transfer among multiple viable euploid embryos could enhance reproductive success.

Study design, size, duration
Throughout the year 2022, a retrospective review was conducted on 428 cycles of single frozen-thawed euploid embryo transfers performed at a single institution, targeting patients aged 35 and older. The study aimed to explore potential differences in clinical pregnancy rates based on embryo grade, embryo freezing date, and embryo selection priority.

Participants/materials, setting, methods
Women ≥ 35 years old with single frozen euploid blastocyst transfer cycles was categorized into three groups: (a) with one blastocyst (1/1), (b) with ≥ two blastocysts having the top-priority(½ or higher), and (c) lower-priority blastocysts (lower than ½) to examine potential differences in clinical pregnancy rates among groups based on embryo characteristics, including Gardner grading and day of embryo freezing. Results highlight the impact of both selection criteria and freezing conditions on pregnancy outcomes.

Main results and the role of chance
This study analyzed a total of 428 frozen embryo transfer (FET) cycles. In the context of frozen-thawed single embryo transfer, the clinical pregnancy rate was 52.2% (128/245) when only one euploid embryo was frozen and subsequently thawed for transfer (a). For cases where two or more euploid embryos were frozen, and embryos with a higher priority (½ or higher) were selected for transfer (b), the clinical pregnancy rate significantly increased to 71.3% (62/87). Conversely, when embryos with a lower priority (lower than ½ in order) were chosen for transfer (c), the clinical pregnancy rate was lower at 38.5% (15/38), indicating a statistically significant difference between the groups (p = 0.001). Categorizing embryos based on Gardner grading, “good” embryos (&gt;3BB) demonstrated a clinical pregnancy rate of 66.8% (141/211), while embryos with lower quality (3BB or below) showed a significantly lower clinical pregnancy rate of 40.6% (88/217) (p &lt; 0.001). The analysis of clinical pregnancy rates based on the embryo freezing day revealed significant differences among embryos freezing on 5 days (71.9%, 133/185), 6 days (39.9%, 71/178), 7 days (25%, 2/8), and thawing PGT-A embryos (38.2%, 21/55) (P &lt; 0.001).

Limitations, reasons for caution
One limitation of this study is its retrospective nature, and the potential confounding effect of the close association between embryo selection and embryo grading. Further analysis will be conducted to confirm correlations and address this potential confounding effect.

Wider implications of the findings
In single euploid frozen embryo transfers, selecting the highest-quality embryo through careful embryo selection remains relevant. Morphological indicators of embryos significantly impact early pregnancy outcomes, highlighting the continued importance of strategic embryo accumulation for enhanced procedural success.

Trial registration number
not applicable