Abstract
INTRODUCTION: It is unclear how various in vitro fertilization cycle characteristics may ultimately influence the fertility outcomes of patients utilizing assisted reproductive technology. This study investigates embryo characteristics to determine which features are most associated with clinical intrauterine pregnancy after frozen embryo transfer. METHODS: This retrospective study evaluates 535 single blastocyst frozen embryo transfers (FETs) in 2022 and received IRB approval from the University of Kansas. Logistic regression analyses were used to evaluate embryo characteristics and likelihood of clinical intrauterine pregnancy (IUP), defined as positive fetal cardiac activity on ultrasound after 12 weeks of gestation. Blastocyst survival (percentage of live cells), blastocoele re-expansion, and morphological grade were evaluated prior to embryo transfer. Significant embryonic parameters included blastocyst developmental stage and blastocyst grade before cryopreservation, usage of preimplantation genetic testing for aneuploidy (PGT-A), post-warm blastocyst survival (percentage of live cells), degree of blastocoele re-expansion, blastocyst grading before transfer, and presence of zona pellucida. RESULTS: Among 535 FET cycles, 257 (48.0%) resulted in clinical IUP. Multivariate logistic regression analysis showed a significant independent influence of blastocyst development time (day 5/6) (odds ratio [OR] 0.571; P=.003), morphological grade before cryopreservation (day 5/6) (OR 0.648; P=.013), usage of PGT-A (OR 1.704; P=.010), and percentage of post-thaw live cells (OR 0.322; P=.001) on embryo transfer success rates. While fully expanded blastocysts showed a significantly higher rate of clinical IUP, the degree of blastocoele re-expansion did not appear to be independently related to ongoing pregnancy when multivariate logistic regression analysis was employed (OR 2.886; 95% CI: 0.824–10.105; P=.097). CONCLUSION: In addition to blastocyst quality prior to cryopreservation, post-thaw blastocyst survival is an independent predictor of embryo recovery and further development potential. Additional understanding of the potential contributors to failed FETs can inform strategies for improvement. Further investigation is needed to determine how to minimize embryonic cell damage during the vitrification and warming process.
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