4 January 2021

The importance of compatibility testing (CGT) for couples

compatibility testing (CGT)
Consultant Gynaecologist
Dr Mireia Galian

IVI London

IVI Birmingham


When couples consider their compatibility, they may think about shared interests and common values. But when it comes to starting a family, it is time to look at a different type of compatibility.

One in every 25 children in the UK is affected by a genetic disorder. In many cases, this is not the result of an obvious risk factor, but an invisible and undetectable genetic defect, passed down unknowingly by the parents. This is caused by both parents carrying a defect within in the same gene. These healthy individuals have no way of predicting this outcome: in many cases, they have no idea they could be heading for a problem.

Compatibility testing allows this scenario to be prevented by testing and assessing each partner for specific genetic defects. If no issues (known as mutations) are identified, then couples can go ahead with confidence knowing that their risk of having a baby affected by serious a health condition is extremely low.


Why choose to have a compatibility test?

It has been estimated that around 4 – 5% of couples share a genetic defect for a recessive health condition. Recessive diseases are difficult to detect without medical assistance. As a couple, both partners can be healthy carriers and unable to predict such condition in their offspring. Being carriers means that both parents carry the same defective DNA in one of the two copies of their genetic makeup. While this has no impact on their life or their own health, the combination of their genes could lead to a 25% chance of their baby being born affected by the condition. In other words, due to the different genetic combinations of their genes, their child has a one in four chance of inheriting two copies of the faulty gene – one from each parent – and manifest such disease.

Although these genetic diseases have no cure, they can be prevented with the use of preliminary compatibility genetic testing (CGT), which provides couples the possibility to assess their risk when it comes to facing this scenario.

The vast majority of couples taking the test will be a good genetic match. Although nothing can be used as a guarantee of a perfectly healthy baby, it can certainly give couples the confidence of knowing that the odds are scientifically in their favour.


How does compatibility testing work?

The test is performed on DNA extracted from a blood sample from each prospective parent. It takes about a month for the analysis to be completed. If the analysis detects that they do not share the same mutation or genetic defect, nothing needs to be done. If the results establish that they do share a genetic defect, this would mean their child risks being born with the genetic disease of which both parents are carriers. In this scenario, couples are equipped with the knowledge they need to make informed decision about their options:

  • IVF treatment with pre-implantation genetic testing (PGT): Even if you know that as a couple you risk passing on a genetic disease to your offspring, there are tests which we can do as part of the IVF process to make sure that only healthy embryos are transferred back into the uterus.
  • Treatment using a gamete, either egg or sperm, from a donor who is not a carrier of the disease in question: Donors can be assessed for genetic compatibility in the same way as it is done with a partner. 

Couples could also decide to go ahead with a naturally conceived pregnancy or prenatal assessment, or pursue alternative routes to parenthood such as adoption or becoming a foster parents.


Who should consider having a compatibility test?

Genetic compatibility testing is recommended in the following circumstances:

  • Before trying for get pregnant naturally. Any couple who wants to start a family can benefit from knowing if they carry a genetic condition which could be passed down.
  • Before any fertility treatment. It can be very useful to have your genetic compatibility results before undergoing treatment, so that risks can be assessed and the appropriate treatment advised.
  • Before any fertility treatment using donor eggs or donor sperm. Donors can be tested to assess genetic compatibility with the recipient of their sperm of oocyte. This allows your consultant to select the better donor that at the same time ensures the lowest risk of endangering a baby affected by a recessive disease.


IVF with pre-implantation genetic testing (PGT-M)

Most of us think of IVF as a method of giving extra help to those who struggle with infertility to have a baby, and this is true. However, the ability to screen and minimize the risk of many life-changing inheritable diseases is another hugely significant medical advance, which would not be possible without the existence of IVF. When using PGT to screen for a recessive disease, here’s how it works:

Step 1:

The IVF process of ovarian stimulation, egg retrieval and fertilisation in the laboratory, using sperm microinjection (ICSI), is followed in the normal way.

Step 2:

Genetic testing is carried out once the resulting embryos reach blastocyst stage (5 days in the culture). In a harmless procedure, a tiny amount of cells are extracted from the embryos. These miniscule samples are sent for analysis as the embryos are frozen.

Step 3:

The genetic testing can confirm the presence of monogenic diseases, but it will also identify numerical alterations affecting the number of copies of chromosomes (which helps us categorise normal/abnormal embryos).

Thanks to the genetic testing, embryos that are free from the specific inheritable disease can be selected. Later on, the one most suitable embryo available will be transferred to the uterus. The remainder can then be frozen for use in the future.


IVI’s excellence in CGT & PGT

IVI has led the field in genetic testing and our dedicated laboratories have become a benchmark in reproductive medicine. As experts in the field, we are often called to share our expertise in carrying out these types of analyses for other fertility clinics and reproductive health centres around the world.

If you are thinking about starting a family and, like us, a healthy baby is top of the list, get in touch via our online contact form about a compatibility test for couples.

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