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What is Trisomy 18?


Trisomy 18

Trisomy 18 (Edwards' syndrome) is a genetic condition caused by the presence of an extra chromosome in the body’s cells. This extra genetic material affects fetal development. This syndrome is not a disease and, except in rare cases, it is not a hereditary condition. Instead trisomy 18 occurs by chance at conception.

Although it's been more than 50 years since researchers first identified the chromosomal nature of trisomy 18, we still don't know what causes the presence of an extra chromosome. It is not something you've done, or not done. It can happen to anyone.


 How many babies are affected?

  • About 1 in every 1,500 pregnancies is diagnosed with trisomy 18. It is the most common autosomal trisomies after trisomy 21 (Down's syndrome).
  • In England and Wales between 2004 and 2011, there were 4,028 diagnosed cases of trisomy 18.
  • In the same 8 year period, 372 babies with trisomy 18 were born alive.

(National Down Syndrome Cytogenetic Register, data provisional).

What is the likely outcome for a baby diagnosed with these conditions?

Parents who receive a diagnosis for their baby are faced with making complex and difficult decisions. You may be asking yourself what the quality of life will be like for your baby. You may also be considering what the impact will be on the whole family as you care for your affected child. Parents often feel that there is little time to gather the information they need to make such life-changing decisions. Download a copy of SOFT UK's Your Unborn Baby

Sadly the risk of miscarriage and stillbirth is high but of the babies who do survive pregnancy, almost 1 in 10 live to celebrate their 1st birthday. Some of these children thrive for many years, even living into adulthood. Read family stories.

Infants with the less common mosaic and partial forms tend to survive for longer - your local genetic service can advise you on an individual karyotype.

Newborns with trisomy 18 are more likely to have significant problems with different organ systems and their care needs are likely to be high. As a parent, you will be learning on the job. Caring for your child.

In Britain, more than 6 in every 10 diagnosed pregnancies will be terminated early. Termination.

When supported by other families, most parents feel that the overall experience of their child's life is positive and that their family is enriched. Read the research.

What is the risk of a pregnancy bring affected?

  • About 1 in 200 births result in a baby with a chromosome defect. 
  • The age of the mother is the major known risk factor for having a baby with trisomy 18. 
  • There is a small increased risk of the same trisomy after a previous pregnancy with trisomy 13 or trisomy 18. There may also be a small increased risk for women with a previous pregnancy with trisomy 21 (Down's syndrome)
  • Except in rare inherited cases, chromosome defects are usually one-off events.

You may wish to discuss the option of prenatal diagnosis if you become pregnant in the future or if you have had a previous pregnancy with a trisomy. 

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