Effects of different embryonic development days on clinical outcomes of freeze-thawed embryo transfer.

Objective: To compare the clinical outcome of freeze-thawed embryo transfer at different embryonic development days in whole embryo freezing patients of different ages.

Methods: This was a retrospective study. Collected clinical data of 558 patients who underwent freeze-thawed embryo transfer at Reproductive Center of Baoding Maternal and Child Health Hospital from March 2019 to January 12, 2022. The enrolled patients were divided into two groups of 21~35 years old group(n=421) and 35~50 years old group(n=137) according to their ages. Then, three subgroups were established according to the development days of the freeze-thawed embryos under different age groups, D3 subgroup, D5 subgroup and D6 subgroup.

Results: There were no significant differences in biochemical pregnancy rate, clinical pregnancy rate, multiple pregnancy rate, abortion rate, among the three groups in the 21~35 years old group. While significant difference was observed the highest embryo implantation rate in D5 subgroup(P<0.05). Meanwhile, in 35~50 years old group, the biochemical pregnancy rate in D5 subgroup was significantly higher than that in D3 and D6 subgroups(P<0.05). The clinical pregnancy rate of D5 subgroup was significantly higher than that of D6 subgroup(P<0.05), and the clinical pregnancy rate of D5 subgroup was higher than that of D3 subgroup(P>0.05). The embryo implantation rate in D5 subgroup was significantly higher than that in D3 and D6 subgroups(P<0.05).

Conclusion: Compared with D3 and D6 transfer strategies, D5-blastocyst transfer exhibits more satisfactory clinical outcomes, with the highest clinical pregnancy and embryo implantation rates.