In order to create embryos for genetic testing, the ovaries have to be artificially stimulated using hormones to produce several eggs at the same time.
Because a significant number of a couple’s embryos are likely to be affected by the genetic or chromosomal abnormality, a large number of embryos need to be created for the best chances of success.
At the appropriate time, the eggs are removed in during a surgical procedure known as egg retrieval. Once the eggs are removed, they are inspected to determine which are mature and normal appearing.
Fertilisation during PGD will be done either by:
. In Vitro Fertilisation (IVF): Sperm and eggs are placed together in a culture dish to allow fertilisation to occur.
. Intracytoplasmic Sperm Injection (ICSI): A single sperm is injected in the centre of an egg. This technique is used for conditions caused by a single faulty gene.
The morning after injection/insemination of the sperm, the embryologist carefully examines each egg to see if fertilisation has occurred.
The eggs that were successfully fertilised are grown in the laboratory for 5-6 days when the embryo forms what is called a blastocyst of about 100-150 cells. At this stage trophectoderm biopsy (the cells which will form the placenta) takes place.
The removal of these cells should not harm the embryo.
The cells are tested to see if the embryo from which they were removed contains the abnormality that causes the genetic condition.
Only those embryos that do not have the specific genetic condition that was tested for will be transplanted into the woman’s uterus. Usually one embryo will be transferred to the uterus at any one time to avoid the possibility of multiple births (more than one baby in a pregnancy).
Any suitable remaining unaffected embryos will be frozen for later use.
Those embryos that are affected by the inherited condition are allowed to perish or couples are asked if they would consider allowing these embryos to be donated for research and training.
Twelve days after the embryo transfer, the woman is given a pregnancy test. A positive pregnancy test means that an embryo has implanted.