Improved pregnancy outcomes with single day 5 blastocyst transfer from post-thawed cleavage embryos in the first transfer cycle: a retrospective propensity score-matched cohort study

Background We aimed to test the hypothesis that transferring blastocysts derived from extended culture of cleavage-stage embryos for single embryo transfer in the first transfer cycle would result in better clinical outcomes than transferring frozen-thawed blastocysts, without affecting neonatal outcomes. Methods We conducted a retrospective propensity score-matched cohort study at a single reproductive medicine center. After excluding transfer cycles that did not meet the inclusion criteria, we classified the subjects into two groups based on the blastocyst transfer strategies. The group receiving blastocysts derived from the extended culture of the frozen-thawed cleavage-stage embryos was labeled the F3T5 group, while the group receiving frozen-thawed blastocysts was labeled the F5T5 group. The primary outcomes of this study were the implantation rate and the ongoing pregnancy rate. Secondary outcomes included the biochemical pregnancy rate, miscarriage rate, clinical pregnancy rate, and neonatal outcomes. Results After propensity score matching, a total of 811 blastocyst transfer cycles were included in the analysis. 307 cycles in the F3T5 group and 504 cycles in the F5T5 group. The results revealed that the F3T5 group had significantly higher rates of biochemical pregnancy (78.83% vs 66.07%, P  < 0.001), clinical pregnancy (70.36% vs 59.72%, P  = 0.029), implantation (70.36% vs 59.72%, P  = 0.036), and ongoing pregnancy (64.17% vs 50.99%, P  < 0.001) compared to the F5T5 group. There were no statistically significant differences between the two groups in terms of multiple pregnancy rate, ectopic pregnancy rate, miscarriage rate, and neonatal outcomes such as gestational weeks, single birth weight, and pregnancy complications ( P  > 0.05). Conclusion Our findings suggested that transferring the single blastocyst derived from the extended culture of the frozen-thawed cleavage embryos in the first transfer cycle might offer a beneficial approach for optimizing assisted reproduction technology success rates in women under 36 years of age without affecting the neonatal outcomes.