About trisomy 18 or Edwards syndrome
Trisomy 18, or Edwards syndrome, is a chromosomal condition. It happens when a baby’s cells have 3 copies of chromosome 18, rather than the usual 2. 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 few survive their first year and beyond.
Sometimes only some of a child’s cells have an extra copy of chromosome 18. This is called ‘mosaic’ trisomy 18. Children with mosaic trisomy 18 can have a milder form of the condition.
For typical human development, we need 46 chromosomes (23 pairs carrying genetic material from each parent) in all of the cells in our bodies. Chromosomal anomalies 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, or Edwards syndrome.
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 the following:
- 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.
The 12-week ultrasound can also show the physical differences that many babies with trisomy 18 have.
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.
If you’re told that your unborn or new baby has trisomy 18, it 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. You can also get support from organisations like S.O.F.T. Australia and Genetic Alliance Australia.
Support and treatment for children with trisomy 18
There’s no cure for trisomy 18, or Edwards syndrome.
If you’re told that your unborn baby has trisomy 18, your midwife, GP or obstetrician or a genetic counsellor will be able to give you information and support. This can help you decide what’s best for you and your family during pregnancy.
When babies are born with trisomy 18, there are often very sad and difficult decisions and choices to be made. This might include a choice between making a baby comfortable and prolonging life through invasive surgery.
Some children with mosaic trisomy 18 live to adulthood. If your child has mosaic trisomy 18, early intervention is the best way to support your child’s development. Early intervention includes therapies, education and other supports that will help your child reach their full potential.
If your baby is diagnosed with trisomy 18 before or after birth, the following professionals might be able to help you:
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.
If women are older when they get pregnant, they have a higher chance 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.