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Trisomy 18 (Edwards syndrome)

9 May 2022

Trisomy 18 is a chromosomal disorder in which a baby has an extra copy of chromosome 18. Babies with trisomy 18 are often stillborn or die shortly after birth. However, some babies with trisomy 18 do survive, but they have severe intellectual disability and physical abnormalities.

What is Trisomy 18?

Trisomy 18, also known as Edwards syndrome, is a chromosomal disorder that occurs when a baby has three copies of chromosome 18 instead of the usual two. This extra chromosome 18 causes severe intellectual disability and physical abnormalities.

Babies born with trisomy 18 often have a small head and jaw, low-set ears, and clenched hands. They may also have abnormalities in the heart, lungs, diaphragm, blood vessels, gut, bones and kidneys. Additionally, they may have difficulty with seeing, hearing and feeding.

Most babies born with trisomy 18 do not live beyond the first few weeks of life. A small percentage survive their first year and beyond. The way a child is affected by trisomy 18 depends on whether all of the child’s cells contain three copies of chromosome 18 or only some of them do. Some children might have only a few features of the condition while other children might have many. Trisomy 18 affects both boys and girls but is more common in girls.

For normal human development, we need 46 chromosomes (23 pairs carrying genetic material from each parent) in all of the cells in our bodies. Chromosomal abnormalities are when there are missing or extra chromosomes or changes in the structure or arrangement of the chromosomes. Trisomy 18 is a chromosomal abnormality that results in an extra chromosome 18. This causes severe intellectual disability and physical abnormalities in those affected. While most babies with trisomy 18 do not live beyond a few weeks, some may survive their first year and beyond. Treatment and prognosis depend on the individual child’s symptoms and how many of their cells are affected by the disorder. If you have any questions or concerns about your child’s development, please consult with your doctor.

What is the testing for Trisomy 18?

Screening tests give you information about the likelihood that your baby has trisomy 18, but these tests don’t give you a definite answer. Examples of screening tests include:

non-invasive prenatal testing (NIPT): you give a small amount of blood, which is tested for parts of your baby’s DNA

first trimester combined screening test: this combines a blood test from you with a measurement from your 12-week ultrasound scan.

Depending on the results of screening tests, you might want to have diagnostic testing. Diagnostic testing can tell you definitely whether your baby has trisomy 18.

Diagnostic tests include chorionic villus sampling (CVS) and amniocentesis. Both of these tests are very accurate, but they also have some risks.

You can talk to your doctor or midwife to get more information about these tests.

If the doctor thinks your baby has trisomy 18, the doctor will confirm this by giving your baby a blood test.

Being told that your unborn or new baby has trisomy 18 can be a big shock for you and your family. Talking with other parents can be a great way to get support. You can connect with other parents in similar situations by joining a face-to-face or online support group. Joining a support group can provide you with information and resources, as well as emotional support.

Some parents choose to end their pregnancy after receiving a diagnosis of trisomy 18. This is a personal decision, and there is no right or wrong answer. If you are considering this option, it is important to talk to your doctor or midwife about all of your options and what they mean for you and your baby. There are also many organizations that can provide support and information.

What therapy and support is available for children with Trisomy 18?

The National Disability Insurance Scheme (NDIS) might support your child with trisomy 18, as well as you and your family. Our guide has answers to your questions about the NDIS.

If your baby is diagnosed with trisomy 18, or Edwards syndrome, before or after birth, the following professionals might be able to help you:

clinical geneticist

genetic counsellor




occupational therapist



speech pathologist.

What causes Trisomy 18?

Trisomy 18, also known as Edwards syndrome, is most often caused by a random error in the formation of a parent’s eggs or sperm. This error can also occur after conception, while the baby is still developing in the womb. The older a mother is when she gets pregnant, the higher her chances of having a baby with trisomy 18. If you have one baby with trisomy 18, your chance of having another baby with the syndrome is usually very low. Genetic testing can give you more information about this.

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