EMBRYO QUALITY AND PREGNANCY RATE (Part 2)

Last week, we discussed embryo grading and quality of division with emphasis on size and level of fragmentation. Today, we will address grading system in various stages of embryo development.

Grading Systems for Day 3 (Cleavage) and Day 5 (Cleavage)
Embryo transfers occur either 3 or 5 days after egg retrieval. Embryos are developmentally different on these days and so we have different grading system for day 3 (Cleavage stage) embryo and day 5 (Blastocyst stage) embryo. Each will be discussed in turn.

The embryo grade refers to how the cells in the embryos look. The system used to grade embryo appearance is presented in this simplified manner for better understanding.

Cleavage Grading:
Grade 1: Cells are of equal size; No fragmentation seen. Embryologist’s first choice for transfer.
Grade 2: Cells are equal size; Minor fragmentation.
Grade 2.6: Cells are equal size; Moderate fragmentation.
Grade 3: Cells are of unequal size; No fragmentation to moderate fragmentation.
Grade 4: Cells are of equal size or unequal size; Fragmentation: moderate to heavy.
The good embryo quality is very important, but sometimes the physically determined worse embryos may result in pregnancy.

Blastocyst Grading:
This is the stage of development usually observed on day 5 and 6 of culture. A blastocyst is characterized by the presence of an inner cell mass, trophectoderm and a blastocoel cavity. It is often referred to as a blast.

The inner cell mass commonly referred to as the ‘’ICM’’ Is the little cluster of cells on the interior of the blastocyst that develop into the actual fetus while Trophectoderm are the cells that surround the outside of the blastocyst; they play a role in implantation and become the placenta.

Several studies have suggested that the pregnancy rate and live birth rate of blastocyst day 5 is higher than a day 3 embryo transfer. This is because blastocyst stage embryo transfer permits the identification of embryos that could maintain their developmental process and thus allows the recruitment of good quality embryos with enhanced developmental ability.

An average of 30 to 50 percent of embryos makes it to the blastocyst stage. The failure of some embryos to make it to the blastocyst stage is most likely due to defects in the embryos. If for example we have ten embryos on day 3 and we select two to transfer, we may not select the right embryos. The probability that we select the three or five that would have gone to day 5 or day 6 is not very high.

The quality of the sperm and egg also impacts on the quality of the embryos and blastocyst formed. Poor quality sperm and egg may result in no fertilization or fertilization may occur with no cleavage and in some cases the embryos may develop to cleavage stage but not able to develop the blastocyst stage. Poor quality blastocyst embryos hardly result in pregnancy and live birth.

The genetic composition of embryos is very important. Genetically, abnormal embryos will often result in recurrent implantation failure and repeated pregnancy loss. The embryo grading system does not answer the question of whether an embryo is genetically normal or not.

More extensive test like the PGT-A (Pre-Genetic Implantation Testing for Aneuploidy), allows genetically healthy embryos to be sorted and transferred to the woman, thus increasing the chance of a healthier pregnancy and live birth.

CONCLUSION
In summary, the quality of embryo is a great factor influencing pregnancy and pregnancy outcome. The quality of the embryo often is the product of the sperm and egg they are formed from. Commencing an IVF treatment your doctor carries out some blood test to determine if you and your spouse are likely to produce a good quality embryos or not.
Age plays a role in the quality and quantity of sperm and egg. Advanced age increases the risk for genetic abnormality and poor embryo quality. Poor quality embryo will often fail to implant and in case where they implant, eventually may result in miscarriages.

Women with advanced maternal age and poor ovarian reserveare often counselled to the use of donor eggs so as to increase their chance of pregnancy and a live birth. In the same vein men with poor sperm quality and quantity who have attempted ICSI (Intra Cytoplasmic Sperm Injection) without success may be counselled to the use of donor sperm.

For couples trying to conceive it is recommended you explore every opportunity in Assisted Conception and Assisted Reproductive technology with the aim of achieving successful pregnancy and healthy live birth.