| Summary: | Abstract Background This study aimed to analyze the clinical outcomes of blastocyst which undergo the preimplantation genetic testing (PGT) transplantation from frozen-thawed D5 and D6. In addition, the effect of blastocyst grade on clinical and neonatal outcomes was also investigated in this study. Methods The pregnancy and miscarriage rates of 1130 cycles of frozen embryo transfer, including 784 D5 frozen embryos and 346 D6 frozen embryos in the Reproductive Hospital of Shandong University from January to December 2020 were analyzed. Gardner blastocyst scoring was used for blastocyst evaluation. Results The pregnancy rate of D5 blastocyst was significantly higher, whereas the miscarriage rate of D5 blastocyst was lower, than that of D6 blastocyst tissue biopsy. No significant difference was observed in birth weight and low birth weight of D5 blastocyst and D6 blastocyst, preterm birth, gestational age, and neonatal sex. Frozen-thawed D5 blastocysts have higher pregnancy success rates and lower miscarriage rates compared to D6 blastocysts. Conclusion Therefore, both blastocyst grade and embryo biopsy date must be considered when transferring frozen embryos.
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