Personalized embryotransfer in consideration with embryonic developmental speed improves reproductive outcomes for patients with recurrent implantation failure.

Aneuploid embryos and the desynchronization between an embryo and the window of implantation (WOI) are considered important factors in implantation failure. However, even with personalized embryo transfers (pET) based on the endometrial receptivity test, the clinical pregnancy rate with euploid embryos is reported to be only about 60%. Failure of pET with an euploid embryo on the day the test recommended may suggest the importance of more precisely synchronizing the blastocyst to be transferred and the WOI. In this study, we evaluate whether pET with good quality blastocysts including euploid embryos, considering embryonic developmental speed, improves the clinical outcomes in recurrent implantation failure (RIF) patients. A total of 1,660 RIF patients, who had 3 or more failed embryo transfers and underwent an endometrial receptivity test, ERPeakSM, were retrospectively reviewed in two private fertility clinics between October 2020 and September 2022. Among patients whose ERPeakSMresults were receptive (R), pET was performed on the day according to the ERPeakSMresults (standard pET), or pET was performed considering developmental speed of the embryos (Tailor-made ET, TmET). Both groups were analyzed for subsequent HRT cycles after ERPeakSM testing. In the TmET group, the grade of blastocyst to be thawed was estimated based on the past embryonic developmental pattern of each patient and the day of transfer was set as follows: 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. Clinical pregnancy rate (CPR) and live birth rate (LBR) were compared for TmET group versus standard pET group with good quality embryos, and a subanalysis of TmET versus standard pET with euploid embryos was also conducted. The statistical analysis was performed by using chi-square analysis with significance determined by a p=0.05. Of 1,660 RIF patients (average age, 39.2 years), ERPeakSM testing showed a displaced WOI result in 919 patients (55.3%) and an R result in 741 patients (44.6%). Among R patients, 92 patients (average age, 37.3 years) received TmET and 373 patients (average age, 38.3 years) underwent standard pET with morphologically good quality embryos. CPR and LBR of the former group were higher (56.5% vs. 35.9%, p < 0.001 and 35.8% vs. 24.7%, p=0.036, respectively) compared to the latter. In subgroup analysis with euploid ET, CPR and LBR of the former group were higher (72.2% vs. 45.6%, p = 0.085 and 66.7% vs. 35.3%, p=0.0406, respectively) compared to the latter. pET of R patients using good quality embryos in consideration with embryonic developmental speed can improve reproductive prognosis.