Tailor-made embryo transfer considering embryonic developmental speed to overcome the dilemma of personalized embryo transfer.

Research question: Does tailor-made embryo transfer (TmET), timed with respect to embryonic developmental speed, affect pregnancy outcomes in patients with recurrent implantation failure?

Design: Among 741 patients identified as receptive through endometrial receptivity testing, the clinical pregnancy rates and live birth rates were retrospectively compared between those who underwent standard personalized embryo transfer and those who underwent TmET in hormone replacement therapy cycles. Personalized embryo transfer was performed according to endometrial receptivity test results (standard personalized embryo transfer group) or considering embryonic developmental speed (TmET group). For TmET, the expansion grade of warmed blastocysts was estimated based on each patient's previous embryonic developmental pattern. The embryo transfer days were set so that estimated blastocyst grades 3, 4, 5 and 6 were transferred on days P+5, P+5.5, P+6.0 and P+6.5, respectively.

Results: In a propensity score matching analysis, the clinical pregnancy rate was significantly higher in the TmET group than the standard personalized embryo transfer group (P = 0.014), whereas the live birth rates were similar between the two groups (P = 0.65). In a subgroup analysis with euploid embryo transfers, the clinical pregnancy rate was significantly higher in the TmET group than the standard personalized embryo transfer group, although there was no difference in live birth rate between the two groups (P = 0.045 and P = 0.057, respectively).

Conclusions: For patients experiencing recurrent implantation failure and identified as receptive through endometrial receptivity testing, subsequent TmET strategies may further enhance pregnancy outcomes.