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. 2023 Apr;43(2):297-303.
doi: 10.1007/s11596-023-2699-4. Epub 2023 Mar 17.

Pregnancy Outcomes for Day 5 Versus Day 6 Single Frozen-thawed Blastocyst Transfer with Different Qualities of Embryos: A Large Matched-cohort Study

Qiong Yu  1 , Hui He  1 , Xin-Ling Ren  1 , Shi-Fu Hu  2 , Lei Jin  3
Affiliations

Pregnancy Outcomes for Day 5 Versus Day 6 Single Frozen-thawed Blastocyst Transfer with Different Qualities of Embryos: A Large Matched-cohort Study

Qiong Yu et al. Curr Med Sci. 2023 Apr.

Abstract

Objective: This study aimed to determine whether the day of blastocyst expansion affects pregnancy outcomes in frozen-thawed blastocyst transfer (FBT) cycles.

Methods: A retrospective match-cohort study was conducted. Patients who underwent blastocyst transfer in frozen-thawed cycles at day 5 or 6 were matched for potential confounding factors. A total of 2207 matched pairs of FBT cycles were included from January 2016 to December 2019 in our Reproductive Medicine Center.

Results: The clinical pregnancy rate (CPR) and live birth rate (LBR) were significantly increased in day 5 blastocyst transfers when compared to day 6 blastocyst transfers, in terms of the same embryo quality. For FBT cycles with good-quality embryo, the CPR at day 5 and 6 was 61.30% and 57.56%, respectively (P=0.045), and the LBR was 44.79% and 36.16%, respectively (P<0.001). For FBT cycles with poor-quality embryo, the CPR at day 5 and 6 was 48.61% and 40.89%, respectively (P=0.006), and the LBR was 31.71% and 25.74%, respectively (P=0.019). The CPR for FBT cycles with good-quality embryo was statistically higher at day 6 than that at day 5 with poor-quality embryo transferred (57.56% vs. 48.61%, P=0.001). Maternal age, anti-Müllerian hormone (AMH), endometrial thickness, embryo quality, and the day of blastocyst expansion were independently correlated with the CPR and LBR. The FBT cycles at day 5 had significantly higher CPR (adjusted odds ratio [OR]=1.246, 95% confidence intervals [CI]: 1.097-1.415, P=0.001) and LBR (adjusted OR=1.435, 95% CI: 1.258-1.637, P<0.001) than those at day 6.

Conclusion: The embryo quality is the primary indicator for FBT cycles. Day 5 blastocysts should be preferred when the quality of embryo at day 5 is the same as that at day 6.

Keywords: clinical pregnancy rate; day 5 versus day 6; embryo quality; frozen-thawed blastocyst transfer; live birth rate.

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