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Genetic testing in pregnancy

FamilyIt is rare that an individual/couple come for genetic counselling and ask about testing a future pregnancy to see if the baby would be deaf or hearing. This is the case for both deaf and hearing parents. Most people who come for genetic counselling when planning a family do so because they want to know information for preparation. Most would not do anything to actively choose whether their child is hearing or deaf.

Rarely, a deaf or hearing individual does ask to have a test in pregnancy and would consider having a termination (ending the pregnancy) if the baby would be born deaf. Many Australian laws relating to abortion are unclear.  Depending on where the individual lived, it is possible that the obstetricians seeing them would agree to a termination of the pregnancy.

It is only possible to have a genetic test in a pregnancy if the gene change causing the deafness in the family has already been found. The most likely gene to be involved is the Connexin 26 gene. Occasionally, a different gene such as the ones causing Usher syndrome or Alport syndrome has been tested and a change found. Genetic testing in pregnancy is not something that would be ‘recommended’ by a genetics professional, it would only be discussed if it was clear that it was something the individual/couple wanted to find out about.

The ways in which a prenatal test is carried out (amniocentesis and chorionic villus sampling (CVS)) both cause a small increased risk of the pregnancy miscarrying. For this reason, they are not usually done for information alone, but only if an individual was considering ending the pregnancy.

Preimplantation Genetic Diagnosis (PGD)

The term ‘assisted reproduction’ means any medical intervention that helps a woman or couple become pregnant if they are experiencing difficulties with this. In most cases, assisted reproduction is completely separate to genetic counselling.

Assisted reproduction includes receiving eggs or sperm from a donor. It also includes IVF (in-vitro fertilization) where a woman’s eggs are fertilized outside the body (‘test-tube’ fertilization) and then one or two embryos placed back in the womb. If a woman or couple need donor eggs, these would have to be fertilized through IVF techniques. If a woman or couple need donor sperm, then IVF does not need to be used, though the insemination is often done in a fertility clinic (artificial insemination).

There is a relatively new procedure where genetic testing and IVF are both involved. This is pre-implantation genetic diagnosis or PGD. IVF techniques are used to fertilize several eggs and then, when the embryos have developed to the stage where there are about eight cells, just one cell is removed from each embryo and genetic testing is carried out on that cell. This determines which embryos have which copies of one particular gene.

This is something that a woman or a couple could choose to have if they wanted to avoid having an embryo implanted that would have a particular genetic condition. A very small proportion of woman or couples would choose to have this and the majority of these are to avoid a serious inherited illness such as muscular dystrophy. Emotionally, PGD is a very big commitment for someone to make as it involves a series of appointments over an extended time. There is about a 1 in 5 chance that the woman or couple will successfully have a baby as a result of the process. PGD is also expensive and currently only offered in private settings in Australia.

In families where changes in the Connexin 26 gene are known to be the cause of deafness, it is now possible to use PGD techniques to look for these changes. It is not possible to do this with any other genes causing deafness at present. It is rare for someone to request to use PGD to select whether their baby is deaf or hearing.

Within the general population and also within those people who have experience of deafness in their family, there are very different and sometimes strongly held views about the use of genetic testing to affect whether future children will be deaf or hearing.

What developments are likely in the future?

At present, most of the research has looked at single genes that can cause hearing loss. More is starting to be understood about the interaction of genes and environmental factors e.g. particular antibiotics or loud noise and causes of deafness where two or more genes are involved. As more single genes that can cause deafness are discovered, it is likely that information will also be found about how they work within the ear.


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Information provided by the National Deaf Children's Society. Reproduced with permission.

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14-Nov-2015 5:55 PM (AEST)