Two days later after the oocytes have been retrieved, the embryos start dividing. They usually consist of 2 or 4 cells, but rarely 6 cells.

From that day, observation under the microscopy doctors or embryologist may notice that not all of the embryos are the same.

Some embryos may divide more rapidly than others. Some may develop less regular cells and smaller fragments.

After the embryos have been rated clinically according to their quality, they can be classified into three (3) categories.

All are likely to lead to pregnancy, but the chance of a successful pregnancy is lower if the embryo quality is inferior or poor.

Those embryos, which divide more rapidly or whose cells are more regular in morphology, are considered with better quality. They have the priority to be transferred into the uterus.