Pre Implantation Genetic Screening (PGS)
This is a procedure which allows the complete screening of all chromosomes in an embryo to ensure the correct number of chromosomes are present. Patients must undergo an IVF cycle utilising ICSI to create embryos. It then involves the removal of 5-10 cells from a Day 5 or Day 6 embryo by a process known as embryo biospy. These cells are then sent for genetic testing. This allows for the selection of embryos with a normal chromosome for transfer to the uterus. While the accuracy of PGS is not 100%, this testing provides a significantly increased chance of establishing a healthy pregnancy and overcomes many of the genetic risks associated with natural conception.
Who would benefit from PGS?
PGS may be useful for:
- women of advance maternal age
- patients who have had ≥ 3 failed IVF attempts
- women who have had ≥ 2 miscarriages
- patients who have a balanced translocation
What are the risks associated with PGS?
Embryo biopsy is a big manipulation of the embryo. Some embryos may be damaged or stressed by the procedure reducing their capacity to implant.
Embryo biopsy involves culturing embryos until day 5 or 6 post-fertilisation, by which time the cells will have differentiated into the inner cell mass (destined to become the body of the embryo) and the trophectoderm (destined to become the placenta). Embryos need to have a clear inner cell mass and a suitable number of healthy trophectoderm cells to be considered suitable for biopsy. The first step involves drilling a hole in the zona on day 3 of development. Following zona drilling, the embryo is returned to the culture media and grown to the blastocyst stage.
By day 5/6, some of the trophectoderm cells should herniate from the hole in the zona. Approximately 5-10 trophectoderm cells can be removed for genetic testing.
There is a very small risk that the cells biospied from the trophectoderm are not representative of all the cells in the inner cell mass. This means that even though the results for the chromosomes in the trophectoderm cells come back as normal, the cells of the inner cell mass may in fact not be or vice versa. The risks of this can be discussed with our clinical geneticist.
Pre Implantation Genetic Diagnosis (PGD)
This is a procedure which allows the complete screening of all embryos to ensure it does not carry a specific genetic defect such as Cystic Fibrosis or Huntingtons Disease. Patients must undergo an IVF cycle utilsing ICSI to create embryos. It then involves the removal of 5-10 cells from a Day 5 or Day 6 embryo. These cells are then sent to a genetics lab off site for testing. This allows for the selection of embryos free of the genetic defect for transfer to the uterus.
While the accuracy of PGD is not 100%, this testing provides a significantly increased chance of establishing a healthy pregnancy and overcomes many of the genetic risks associated with natural conception.
What are the risks associated with PGD?
Embryo biopsy is a big manipulation of the embryo. Some embryos may be damaged or stressed by the procedure reducing their capacity to implant.
Embryo biopsy involves culturing embryos until day 5 or 6 post-fertilisation, by which time the cells will have differentiated into the inner cell mass (destined to become the body of the embryo) and the trophectoderm (destined to become the placenta). Embryos need to have a clear inner cell mass and a suitable number of healthy trophectoderm cells to be considered suitable for biopsy. The first step involves drilling a hole in the zona on day 3 of development. Following zona drilling, the embryo is returned to the culture media and grown to the blastocyst stage.
By day 5/6, some of the trophectoderm cells should herniate from the hole in the zona. Approximately 5-10 trophectoderm cells can be removed for genetic testing.
There is a very small risk that the cells biospied from the trophectoderm are not representative of all the cells in the inner cell mass. This means that even though the results for the chromosomes in the trophectoderm cells come back as normal, the cells of the inner cell mass may in fact not be or vice versa. The risks of this can be discussed with our clinical geneticist.
