Associations of post-warming embryo or blastocyst development with clinical pregnancy in vitrified embryo or blastocyst transfer cycles

Objective: To investigate whether the degree of post-warming embryo or blastocyst development is associated with clinical pregnancy in vitrified embryo or blastocyst transfer cycles. Methods: Ninety-six vitrified cleavage-stage embryos and 58 vitrified blastocyst transfer cycles were selected. All transfer cycles were performed from February 2011 to March 2019, and all vitrified embryos or blastocysts were warmed from 4 PM to 6 PM and then transferred the next morning from 9 AM to 10 AM. The scores of the cleavage-stage embryos and blastocysts were assessed at warming and at transfer using the modified Steer method and the Gardner method, respectively. The mean embryo or blastocyst score, score of the single top-quality embryo or blastocyst, and the difference in the score between warming and transfer were compared between nonpregnant and pregnant women. Results: In the cleavage-stage embryo transfer cycles, both the top-quality embryo score at transfer and the difference in the score between warming and transfer were significantly associated with clinical pregnancy. A top-quality embryo score at transfer of >= 60.0 (area under the curve [AUC], 0.673; 95% confidence interval [CI], 0.531-0.815) and a difference in the score between warming and transfer of >= 23.0 (AUC, 0.675; 95% CI, 0.514-0.835) were significant predictors of clinical pregnancy. In blastocyst transfer cycles, the top-quality blastocyst score at transfer was the only significant factor associated with clinical pregnancy. A top-quality blastocyst score at transfer of >= 38.3 was a significant predictor of clinical pregnancy (AUC, 0.666; 95% CI, 0.525-0.807). Conclusion: The top-quality embryo score at transfer and the degree of post-warming embryo development were associated with clinical pregnancy in vitrified cleavage-stage embryo transfer cycles. In vitrified blastocyst transfer cycles, the top-quality blastocyst score at transfer was the only significant factor affecting clinical pregnancy.