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Genetic testing for parents who know they could pass on a genetic condition

Some women and couples will be aware that there is a chance that they may pass on a genetic condition to their child. This might be because they have a genetic condition themselves or they know they carry a genetic change that could be passed on. The following information is an overview of what is available and not designed to replace expert guidance and advice from a clinical geneticist or genetic counsellor.

1. Tests in a naturally conceived pregnancy

Non-invasive prenatal diagnosis (NIPD) is available for some inherited single gene disorders (see previous section). Check with a genetic counsellor to see if this could be a testing option. NIPD can usually be done from 10 weeks of pregnancy.

In most cases, the only way to find out if a genetic condition has been passed on to the baby will require an invasive procedure such as CVS or amnio. CVS can be done from 10 weeks and amnio after 15 weeks into the pregnancy. The type of test performed on the sample from either procedure and the time it takes to get a result will depend on the individual case. A clinical geneticist or genetic counsellor will be able to advise on this.

2. Tests available if the pregnancy is achieved through assisted conception (e.g. IVF) – (preimplantation genetic testing)

Some couples are unable to conceive naturally or may want to avoid the possibility of termination of pregnancy. This may lead to them turning to IVF. It is not always possible to get IVF and PGD funded by the NHS and in the private sector the average cost of one cycle of IVF is over £5000. Testing an embryo before it is implanted will usually add at least £2000 and often more to the cost.

It is important to note that IVF does not always result in a successful pregnancy. The most up-to-date success rates can be found on the Human Fertilisation and Embryology Authority (HFEA) website: https://www.hfea.gov.uk/treatments/explore-all-treatments/in-vitro-fertilisation-ivf/

Preimplantation genetic testing involves removing a small number of cells from the embryo, very occasionally the embryo may be damaged as a result. This might be important to consider if it is the last remaining embryo that it is to be transferred.

Testing an embryo:

Testing an embryo

Pre-implantation genetic screening (PGS) also known as pre-implantation genetic testing for aneuploidy (PGT-A)

In order to carry out PGS, a single cell or a small number of cells is removed from the embryo. The DNA of these cells is then tested for chromosomal conditions using a technique such as microarray or sequencing. Only embryos thought to be without chromosomal anomalies are placed back in the womb.

There are no accurate statistics to say exactly how successful PGS might be in improving the chances of an ongoing pregnancy. It is also not 100% accurate so does not completely rule out having a baby with a chromosomal condition. PGS is not available in the NHS.

Pre-implantation genetic diagnosis (PGD) also known as pre-implantation genetic testing for monogenic disorders (PGT-M)

PGD is available on the NHS for certain serious inherited genetic conditions. By law, the HFEA must approve a genetic condition before PGD can be performed on an embryo. So far around 600 conditions have been approved and this list is being updated all the time. The list can be found here: https://www.hfea.gov.uk/pgd-conditions/

An IVF clinic must be licensed by the HFEA to offer PGD. If a genetic condition does not appear on the HFEA list, a licensed clinic can apply on a woman/couple’s behalf to have it added. It takes two to three months for the HFEA to make a decision.

Cells are carefully removed from the embryo in the early days of its development and analysed in the laboratory to see whether the inherited single gene disorder is present. Although clinics quote accuracy of 98-99% for most couples, CVS or amnio will still be offered, if the pregnancy proceeds, to give a definitive yes/no answer.