Purpose: This retrospective cohort study determined the relative efficacy of blastocyst and cleavage-stage transfers in patients with differing numbers of zygotes.
Methods: A total of 1116 women whose embryo transfers were planned independently of patient characteristics were included. Cleavage-stage (D3) and blastocyst-stage (D5) transfer outcomes were analyzed per number of zygotes. The D5 group included transfer cancellations as the intention-to-treat population. The effect of the embryo transfer date on the clinical outcomes (clinical pregnancy and implantation rates) was analyzed using multivariate logistic regression.
Results: Among the patients, 584 and 532 underwent D3 and D5 embryo transfers, respectively. The clinical pregnancy rates were significantly higher in D5 patients with ≥ 6 zygotes (25.7% vs 48.3%). The multivariate logistic regression analysis for clinical pregnancy did not show significant differences between the blastocyst and cleavage-stage transfers in patients with ≤ 5 zygotes (0.874 [0.635-1.204]). Compared to the cleavage-stage, blastocyst-stage transfers for patients with ≥ 6 zygotes resulted in a three-fold increase in clinical pregnancy rates (3.122 [1.797-5.425]).
Conclusion: Blastocyst transfers were not inferior to cleavage-stage embryo transfers among patients with few zygotes and were preferable for patients with several zygotes.
Keywords: Blastocyst-stage transfer; Cleavage-stage transfer; Clinical pregnancy; Implantation; Zygote.
© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.