P-250 Only euploidy does not ensure optimal chances for successful live birth through single blastocyst cryotransfer

Abstract Study question What does a euploid blastocyst require to provide the greatest probability of successful birth? Summary answer Morphokinetic and morphological features of the inner cell mass (ICM) and trophectoderm (TE) are crucial for optimizing live birth chances in cryo-transferred euploid blastocysts. What is known already Embryo selection through preimplantation genetic testing for aneuploidy (PGT-A) alongside frozen embryo transfer strategy enhances outcomes of single-embryo transfer cycles. While euploidy is a crucial indicator, investigations on the identification of additional criteria influencing implantation and live birth rates remain imperative. Studies suggest morphokinetic and morphological quality may supplement predictive factors for euploid embryo success, with varying correlations. The impact of factors like age or gamete origin on euploid blastocyst success remains uncertain, differentiating it from clear effects on non-diagnosed embryos. Optimizing selection criteria involves navigating the intricate interplay of these variables. Study design, size, duration This retrospective study analyses the pregnancy rate (PR) in 596 single embryo cryotransfers of full euploid blastocysts (without detected mosaicism) between February 2019 and September 2023. From these, 437 had a known outcome, and the live birth rate (LBR) was calculated. The study explored the potential impact of gamete origin, oocyte provider age, recipient age, morphokinetics, and morphological quality of ICM or TE (Gardner score) on the reproductive success of the transferred embryo. Participants/materials, setting, methods All embryos were biopsied at the blastocyst stage and successively vitrified. High-resolution next-generation sequencing was used for PGT-A. Only deferred transferences of single post-thawing intact embryos were included. Morphokinetic was assessed using the KIDscoreD5 3.1. Quantitative variables (oocyte provider age, recipient age, and morphokinetic score) were compared using the t-student test, while qualitative variables (gamete origin, morphological quality of ICM and TE) were assessed using the chi-square test. Main results and the role of chance Oocytes leading to pregnancies and live births were derived from women with ages comparable to those without success (Pregnancy: 30.0±7.1 vs. 30.8±6.8, p = 0.174; Live Birth: 30.1±7.1 vs. 30.5±6.9, p = 0.499). Similar age was also observed among recipients achieving pregnancy (41.5±5.4) and live births (41.1±5.1) compared to those who did not (Pregnancy: 41.8±5.1, p = 0.506; Live Birth: 41.5±5.3, p = 0.411). The origin of oocytes and semen (own or donor) did not significantly affect PR (Oocytes: 199/273 vs. 217/323, p = 0.130; Semen: 328/473 vs. 88/123, p = 0.224) or LBR (Oocytes: 113/205 vs. 116/232, p = 0.285; Semen: 183/347 vs. 46/90, p = 0.783). Morphokinetics played a crucial role, with euploid embryos resulting in pregnancy (7.5±1.7) and live births (7.6±1.6) exhibiting significantly higher scores than those without success (6.9±1.7; 7.1±1.7; p 0.05).199 ICM quality did not significantly impact PR (A:211/296, B:190/275, C:15/25; p = 0.469). However, higher miscarriage rates in C-quality ICM blastocysts significantly reduced the LBR (A:116/211, B:107/205, C:6/21; p 0.05). TE quality exhibited significant differences in PR (A:221/289, B:184/289, C:11/18; p 0.05). Since the miscarriage rate was similar among groups (p = 0.787), LBR remained higher in A-quality TE blastocysts (A:124/209, B:98/213, C:7/17; p 0.05). Limitations, reasons for caution As a retrospective analysis, this study is inherently limited. The influence of expansion grade on success rates remains unexplored, given the use of assisted hatching on day 3 of culture. Performing assisted hatching at the time of biopsy could potentially overcome this limitation. Wider implications of the findings The pursuit of a euploid embryo often becomes the priority in IVF laboratories. However, once the milestone is achieved, morphokinetics and embryonic morphological quality must continue to be considered. This study provides valuable insights for conveying a detailed message to patients with euploid embryos about their prospects for homebirth success. Trial registration number not applicable