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?
- 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) enables people with an inheritable condition in their family to avoid passing it on to their children. It involves checking the genes and/or chromosomes of embryos created through IVF.
Is PGD for me?
Your specialist may recommend PGD if:
- you have ended previous pregnancies because of a serious genetic condition
- you already have a child with a serious genetic condition
- you have a family history of a serious genetic condition, or
- you have a family history of chromosome problems.
Which genetic conditions can be tested for during PGD?
PGD can be used to test for virtually any genetic condition where a specific gene is known to cause that condition. It is currently approved to screen for over 250 genetic conditions.
To see the types of conditions that may be tested for, see the HFEA’s list of PGD conditions:
If you want to screen for a condition which has not be approved, your clinic will need to make an application to the HFEA. For it to be approved, we must, by law, agree that the genetic condition meets certain criteria (including that it is serious enough).
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 visit ‘Choose a Fertility Clinic’
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 usually 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 to 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. The embryo unaffected by the condition is transferred to the womb to allow it to develop.
Step 6. Any suitable remaining unaffected embryos can be frozen for later use (see p71). Those embryos that are affected by the condition are allowed to perish or, with your consent, used for research (see p83).
It is possible that, instead of removing and testing one or two cells from a two to three-day-old embryo, some clinics may allow the embryo to develop to five to six 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 only affect one sex rather than the other. Examples include Duchenne muscular dystrophy, which affects boys but not girls. (Girls may still ‘carry’ the gene for the disease but they will not suffer from it). In these sorts of cases, the embryo is tested to find out its sex and only embryos of the non-affected sex are transferred to the womb. In the UK, sex selection is only allowed to avoid having a child with a serious medical condition; it is illegal to carry out sex selection for social reasons (e.g. for family ‘balancing’).
How does sex selection work?
The procedure for carrying out sex selection is likely to be as follows:
Step 1: You undergo normal IVF treatment to collect and fertilise your eggs.
Step 2: The embryo is grown in the laboratory for a number of days.
Step 3: A trained embryologist removes a number of cells from the embryo.
Step 4: The chromosomes are examined to identify which embryos are male and which are female.
Step 5: One, two or three of the embryos of the appropriate sex are transferred to the womb so that they can develop. Any remaining embryos of the appropriate sex can be frozen for later use.
However, embryos that have been biopsied may not be suitable for cryopreservation and use in subsequent treatment cycles.
Step 6: The embryos of the different sex are allowed to perish or may be used for research or training (with your consent).
What are the risks of sex selection?
Most of the risks involved in sex selection treatment are similar to those for conventional in vitro fertilisation (IVF). For more information, see:
With sex selection, there is also the possibility that:
- some embryos may be damaged by the process of testing
- no embryos are suitable for transfer to the womb after sex selection (i.e. all embryos are of the sex being selected against)
- the test is not 100% reliable.
New genetic testing techniques
Some scientists are developing genetic tests that look for the specific genes that cause sex-linked disorders, such as Duchenne muscular dystrophy or Haemophilia A.
This means that as well as selecting all female embryos, you may also be able to select male embryos that do not carry the gene for the disease.
For more information contact your clinic.
Page last updated: 01 April 2014