Pre-implantation genetic diagnosis (PGD)
- What is PGD?
- Is PGD for me?
- Which genetic conditions can be tested for during PGD?
- Which clinics carry out PGD?
- Case by case licences
- What are the risks of PGD?
- How does PGD work?
- What is the chance of having a baby with PGD?
- PGD - starting the process
- Sex selection
What is PGD?
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.
Is PGD for me?
Genetic testing of your embryos may be recommended if:
- you have had a number of abortions because your baby had a genetic condition
- you already have a child with a serious genetic condition
- you 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. To see the types of conditions that may be tested for, see the HFEA’s list of PGD conditions:
The HFEA must agree that a particular genetic condition is sufficiently serious before clinics are permitted to test for that condition using preimplantation genetic diagnosis (PGD).
Even if the HFEA approves the genetic condition for testing, clinics must make their own judgment on whether PGD is the appropriate treatment for a particular patient. In doing this, they will use the guidance contained in the HFEA’s Code of Practice. This guidance requires them to take into account the view of that patient of the seriousness of the condition to be avoided.
PGD is an area of medicine that is rapidly developing, so new tests often become available. If a condition is not approved by the HFEA, we recommend getting in touch with a licensed PGD clinic to see whether they are prepared to make an application for that condition to be approved.
Which clinics can carry out PGD?
A clinic must have a licence from the HFEA to carry out PGD testing. The licence allows the clinic to test for any condition or combination of conditions that appear on the HFEA’s list of PGD conditions. Some clinics will have particular experience of testing for some conditions.
To find clinics in the United Kingdom that are licensed for PGD, and the tests they have experience of, visit ‘Choose a Fertility Clinic’
‘Case by case’ licences
Most of the genetic conditions approved by the HFEA can be carried out for any patient who requests it, after following the guidance in the Code of Practice.
However, in cases involving HLA tissue typing, the HFEA only approves PGD on a case by case basis. In these cases, the clinic must apply to the HFEA to authorise testing for a particular patient or family.
Conditions involving HLA tissue typing which must be licensed on a case by case basis are indicated as such on the list of conditions.
Most of the risks involved in PGD treatment are similar to those for conventional IVF. For more information, see:
With PGD, there is also the possibility that:
- 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. You undergo normal in vitro fertilisation (IVF) treatment to collect and fertilise 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.
It is possible that, instead of removing and testing one or two cells from a 2-3 day old embryo, some centres may allow the embryo to develop to 5-6 days, when there are 100-150 cells.
At this stage, cells within an embryo have separated into two types: cells which will form the fetus (inner cell mass) and cells which will form the placenta (trophectoderm).
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 fertilised in the first place
- removing the cells to be analysed damages the embryos
- all the embryos are affected by the genetic disease.
PGD - starting the process
If you are considering this treatment, you should talk to your GP to go through the options available, Your GP can also refer you to see a specialist at your local hospital or fertility clinic.
Access a list of Genetic Centres and Services in your area by visiting the Genetic Interest Group website.
Some genetic diseases, such as Duchenne muscular dystrophy, are sex-linked disorders, which affect boys but not girls (girls may still ‘carry’ the gene for the disease but they will not suffer from it). In this case the cells are examined to find out the embryo’s sex and only female embryos are transferred to the womb.
The sex selection procedure is only allowed to avoid having a child with a serious medical condition, not to have a baby boy or girl to balance your family.
Page last updated: 14 February 2013