What is pre-implantation genetic diagnosis?
- Pre-implantation genetic diagnosis (PGD) is a technique that enables people with a specific inherited condition in their family to avoid passing it on to their children. It involves checking the genes of embryos created through IVF for this genetic condition.
- Pre-implantation genetic diagnosis involves carrying out tests on embryos created through in vitro fertilization (IVF) or intra-cytoplasmic sperm injection (ICSI) to detect certain inherited conditions or abnormalities.
- This helps to ensure that only unaffected embryos are selected before they are transferred to the womb.
- Conventional pre-natal tests for genetic diseases cannot be carried out until the 12th week of pregnancy.
- Testing embryos before they are implanted could help you and your partner to avoid having to make the difficult decision whether to have an abortion if either of you is the carrier of a genetic condition and the embryo is affected.
What are the indications for PGD?
Genetic testing of the embryos may be recommended if:
- Women have had a number of abortions because possible genetic condition in the baby
- If the couple already have a child with a serious genetic condition
- If either of the or one of couple have a family history of a serious genetic condition
Which genetic conditions can be tested for during PGD?
- PGD can be used to test for over 100 genetic conditions, but commonly tested chromosomes are 21,18,13 and sex chromosomes. This procedure may also be called Pre-implantation genetic Screening (PGS).
What are the risks of PGD?
- Most of the risks involved in PGD treatment are similar to those for conventional IVF
- Some embryos may be damaged by the process of cell removal
- Testing may not be 100% reliable or conclusive
How does PGD work?
The procedure for PGD is likely to be as follows:
- Step 1. Couple undergoes You undergo normal in vitro fertilization (IVF) treatment to collect and fertilize your eggs.
- Step 2. The embryo is grown in the laboratory for two - three days until the cells have divided and the embryo consists of around eight cells
- Step 3. A trained embryologist removes one or two of the cells (blastomeres) from the embryo.
- Step 4. The cells are tested to see if the embryo from which they were removed contains the gene that causes the genetic condition in the family
- Step 5. Embryos unaffected by the condition are transferred to the womb to allow them to develop
- Step 6. Any suitable remaining unaffected embryos can be frozen for later use. Those embryos that are affected by the condition are allowed to perish
- Step 7. About two weeks after the embryo transfer, the woman is given a pregnancy blood test
What is the chance of having a baby with PGD?
It is difficult to assess success rates for PGD because there is currently little data available. Most women use this treatment not because they have fertility problems but because they want to avoid having a child with a genetic disease.
- As with most fertility treatments, success depends on many factors, including the woman's age and whether a cause of infertility has been identified
Sometimes no embryos are suitable for transfer to the womb, for reasons including:
- Not enough eggs are produced or fertilized in the first place
- Removing the cells to be analysed damages the embryos
- The genetic disease affects all the embryos.
- The percentage of cycles started that resulted in a live birth was:
- 28 for aged women under 35
- 25 for women aged between 35-37
- After 37 years of age results very variable