During the process of IVF, the embryos are cultured for around six days and during that period they receive quality grades everyday.
Egg Retrieval and Insemination Day 0
Maturity of the egg is important as a mature egg has the best chance of getting fertilized. The three different stages of egg maturation are:
- Germinal vesicle (GV): It is the stage where the egg has not begun meiosis till now and is thus considered immature.
- Metaphase I (MI): This is the first phase of the egg that is meiosis; but is not completely mature yet as it has not entered the second phase of meiosis. This type of immature egg matures after being in temperature-controlled incubation for a couple of hours.
- Metaphase II (MII): This is the second phase of meiosis of the egg, which is mature by now. Eggs at this stage are ready for fertilization and have following characteristics.
Good
- Clear cytoplasm/normal shape
- Single differentiated polar body
- Thin/clear zona pellucida
Fragmented/abnormal polar body
- Slightly pigmented/amorphous zona
- Fragmented/abnormal polar body
- Slightly pigmented/amorphous zona
- Cytoplasmic bodies
- PV debris
Poor
Dark/grainy cytoplasm/misshapen
- Dark/grainy cytoplasm/misshapen
- >1 polar body structure
- Pigmented/thickened zona
- Vacuoles
- PV debris
Fertilization Check Day One
Fertilization can be seen clearly after 16 to 22 hours after the process of insemination. Normal fertilization can be seen by exactly two pronuclei in the center of a one celled zygote. Fertilization is not abnormal when there is a single pronucleus and when there are more than two pronuclei present.
Multicell Grading Day Two/Three
On day two the single cell zygote should divide into an embryo (approx. two to four cells). On day three the embryo should continue to divide (four to eight cells).
Embryo Quality:
- Good: have a clear cytoplasm with symmetrical cells
- Fair: these cells are slightly asymmetrical having slight cytoplasmic irregularities
- Poor: these cells are quite asymmetrical and might have grainy and dark cytoplasm
- A = No fragmentation
- B = <10% fragmentation
- C = 10-35% fragmentation
- D = >35% fragmentation
Day Four
On the 4th day, the transition of embryos begin from a multi cell embryo to a highly advanced developmental stage. Embryos then start compacting and forming morulae. Cells of a morula-stage embryo are not quite distinct like the previous days; and hence these embryos fail to receive quality grades.
Day Five/Six Blastocyst Stage
A blastocyst is developed embryo that comprises of two different cell types: one group of cells is referred as the inner cell mass, that forms the fetal tissue and another group of cells, known as the trophectoderm, helps in the formation of placenta. Blastocysts are graded on the basis of their expansion (early, expanding, expanded, and hatching) as well as on the basis of the quality of these two different cell types (graded on a good-fair-poor scale). Blastocysts that are are good or even fair in quality can be freezed.