1) What is trophectoderm biopsy?
Once the embryos have reached the blastocyst stage on the fifth or sixth day of development, the trophectoderm cells, which will be destined to be placenta, are removed. The removed cells can be tested for comprehensive chromosomal screening (CCS) or specific genetic diseases.
2) What is blastomere biopsy?
The embryos have reached the cleavage stage on the third day of development. Embryos that contain 6 to 8 cells can be biopsied. Each cells are called blastomere. Removal 1 or 2 cells on cleavage stage embryos can be done for CCS or preimplantation genetic diagnosis.
3) Why trophectoderm biopsy?
At the blastocyst stage, embryos contain more than 100 cells. The cells are divided into trophectoderm cells, that will destine to be the placenta, and the inner cell mass, that will destine to be the baby. Removal of 3-5 trophectoderm cells has less impact to the inner cell mass. Compared with the day 3 embryos, which contain only 6 – 8 cells, removal of 1 or 2 cells has higher negative impact to the development and implantation of the embryos. The implantation rate in embryos after blastomere biopsy is less than those after trophectoderm biopsy by 20%.
4) Advantages of trophectoderm biopsy and PGD success rate?
Trophectoderm biopsy increase PGD success rate because the embryos are much less traumatized from this procedure, there is little or no impact to the implantation potential. Removal 3 – 5 cells from blastocysts compared with 1-2 cells from cleavage stage embryos, more cells are available for analysis, which lead to more reliable diagnosis in PGS or PGD. With extended culture, only competent embryos that reach the blastocyst stage are biopsied, so the success rate is higher after embryo transfer.
5) Disadvantage of trophectoderm biopsy?
At this moment, chromosome and genetic analysis requires 24 – 48 hours, so fresh transfer cannot be done because the results are not finished. The reliable cryopreservation technique has to be applied for future transfer. In some couples with poor quality embryos, there is a chance that no embryo develops to blastocyst stage.
6) How is trophectoderm biopsy done?
Laser assisted hatching is done on the good quality embryo to create small hole at the shell. The pipette is used to detach a few cells off the trophectoderm part with help from the laser. After those cells are removed, the biopsied embryo is frozen by Vitrification tec.
7) How is PGS or PGD done with blastocysts?
The trophectoderm cells are removed from the blastocyst, then the DNA is extracted and increased by Whole Genome Amplification (WGA). For CCS-PGS, the genetic materials are tested with Next Generation Sequencing (NGS) or array CGH In the couples who have structural chromosome abnormalities, aCGH is used to checked the unbalanced embryos If the couples are the carriers or affected by single gene diseases, preimplantation genetic diagnosis will be done to identify the unaffected embryos for transfer.