Trisomy 18 (Edwards syndrome)

Trisomy 18 (Edwards syndrome)

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About trisomy 18 or Edwards syndrome

Trisomy 18, or Edwards syndrome, is a chromosomal disorder. It happens when a baby's cells have three copies of chromosome 18, rather than the usual two. The extra chromosome 18 causes severe intellectual disability and physical abnormalities.

Babies born with trisomy 18, or Edwards syndrome, often have:

  • low birth weight
  • a small head and jaw
  • low-set ears
  • clenched hands
  • abnormalities in the heart, lungs, diaphragm, blood vessels, gut, bones and kidneys
  • difficulty with seeing, hearing and feeding.

Most babies born with trisomy 18 don't live beyond the first 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 their cells. Some children might have only a few features of the condition, and 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.

Diagnosis of trisomy 18

You can have tests during pregnancy to help you find out whether your baby has trisomy 18.

Screening tests give you information about how likely it is 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.

Trisomy 18 can also be diagnosed at birth because there are key physical features that your doctor can see. 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.

Support and treatment for children with trisomy 18

There is no cure for trisomy 18, or Edwards syndrome.

Doctors and parents often have to make difficult decisions about treatment. Many parents need to make a very difficult choice between making their baby comfortable and prolonging life through invasive surgery.

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
  • GP
  • midwife
  • obstetrician
  • occupational therapist
  • paediatrician
  • physiotherapist
  • speech pathologist.

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.

Causes of trisomy 18

Trisomy 18, or Edwards syndrome, is most often caused by a random error in the formation of a parent's eggs or sperm.

Less often, this error occurs 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.