The number of day 2 4-cell embryos is link with available blastocysts and live birth rate

Abstract Purpose: The aim of study is to assess the associations between the number of day 2 4-cell embryos (D2-4C) and the subsequent ability of available blastocysts and pregnancy outcomes in natural cycle IVF.. Methods: This study was a retrospective cohort study for couples with infertility treatment between October 2017 and December 2020. The number of D2-4C was recorded during the 948 blastocyst culture cycles in the study. Additionally, the number of D2-4C were analyzed with regard to their live birth rate during 685 double cleavage embryo transfer cycles and 145 single blastocyst transfer.Results: Our fndings showed the number of D2-4C was positively correlated with the number of available blastocysts (r = 0.752, p < 0.001), and have the highest prediction effect on available blastocysts, with an area under the curve (AUC) (95% CI) = 0.861 (0.826-0.896). Thus, the cut-off point was founded to be 4.5, especially in younger than 25 years old, AUC = 0.927. The live birth rate varied significantly according to D2-4C number, with the rate of 17.6%, 33.0% and 36.8% for zero 4-cell embryos, one 4-cell embryos and two 4-cell embryos groups, respectively (p < 0.01). Additional, with the percentage of 1.82%, 5.45% and 92.73% for zero 4-cells, one 4-cells and two 4-cells groups in twin cycle, respectively (p 0.05), however the twin rate increased significantly in double D2 - 4C groups (33.0% vs. 2.0%; p < 0.01).Conclusion: The number of D2-4C was related to increase of available blastocysts and live birth rate, and two D2-4C increase twin rate in double cleavage embryo transfer cycles.