After the completion of insemination process by IVF or ICIS, the eggs are fertilized culturally in the laboratories for three to five days. Then the embryos are graded by the specialized embryologist and then transferred into the women’s uterus. The main criteria used to grade embryos are:
- The number of cell that embryo contains
- The amount of fragmentation that the embryos show
The grade of the embryo provides the information about the chances of becoming pregnant. This embryo grading process is mainly used to determine which embryo should transfer or freeze or which embryos need to discard. This grading system generally will perform on day 3 and day 5 based on the developmental procedure.
Embryo grading- Day 3
The embryos are referred as cleavage stage embryo on day 3 as the cells in the embryo starts dividing. At this stage the embryo size is very less and it needs to grow. The genetic material in the embryo represents the cell division, but the embryo volume does not differ from the volume of the un-fertilized egg. In the embryo, one cell becomes two, two cells become four and four cells become 8 and so on. Sometimes embryos divide a small portion of cytoplasm called as a fragment. The formation of too many fragments in an embryo is simply a disadvantage.
At day 3 the embryos are graded using two criteria: number of cells present in the embryo and their appearance. Typically a day 3 embryo should contain 6 to 10 cells. While the cell number is the objective, the score is given to that embryo between 1 and 4. The grade depends on the look of the embryo: grade one refers that the embryo contains all identical cells of same size with absence of fragmentation.
Embryo grading- Day 5
On day 5, the embryos start dividing into multiple cells and the cell number increases gradually. The divided cells have grown up and started differentiating into specific cell types called blastocyst. This embryo started growing inside the zona pellucida. The cells start to increase and this ZP prepares for development stage for implanting the burst blastocyst into the uterine lining. Embryo grading is a tool that the physicians and embryologists use along with a patient’s age, fertility history, and other information to conclude the most favorable day of transfer, the suitable number of embryos to transfer, and precisely which embryos to transfer.