Although the quality of 4BC blastocysts is not the best quality, the overall quality is okay and their success rate of transfer is relatively high. The quality of 4BC embryos can be understood from the following three aspects: 1. 4 represents the speed of development, and a transfer that reaches grade 3 or higher has a chance of success. The second letter represents the development of the fetus, which is divided into three levels: ABC, B, which is an intermediate level, and B, which refers to the low number of cells and loose arrangement. 3, the third letter represents the condition of the placenta, which is also divided into three levels: ABC, and 3, which represents the loose epithelial cell layer. So, all together, 4BC blastocysts are not the best quality, but they also belong to the successful culture, and their can be transferred.