Trisomy 18, also called Edwards’ syndrome, is not usually expected, or even thought of, in most pregnancies. Unfortunately for some, though, it might be detected in prenatal screening.
If you are in this small group of those diagnosed with this genetic condition, it will be vital to have accurate information and lots of support. Seek out genetic counselors and social workers, if you haven’t done so already, as they will help you understand Trisomy 18 and provide the support you need.
What is Edward’s syndrome or Trisomy 18?
Trisomy 18, also called Edward’s syndrome, is caused by an extra copy of chromosome 18. The trisomy 18 mutation spontaneously occurs at conception, when the father’s sperm cell fertilizes the mother’s egg cell. Usually, each egg and sperm cell contains 23 chromosomes – a total of 46 chromosomes. Babies diagnosed with Edwards’ syndrome (Trisomy 18) have three copies of chromosome 18 instead of two.
You might want to know the risk of birth defects for your unborn baby.
Screening for Trisomy 18, usually completed in the first-trimester, might include a blood sample, or ultrasound used to detect Trisomy 18 early in the pregnancy.
In the second trimester, you might have a blood test and/or CVS (chorionic villus sampling) and amniocentesis, where a sample of amniotic fluids taken.
The screens and diagnostic tests can also check for other genetic conditions, such as Patau syndrome (known as Trisomy 13) and Down syndrome.
Unfortunately, there is no treatment for Edwards’ syndrome and it is usually fatal before birth. Babies who are born with Trisomy 18 have a limited life expectancy.
What is the difference between Trisomy 18 and Trisomy 13?
The word trisomy indicates that any person has 3 of a particular chromosome rather than 2.
As with Trisomy 18, Trisomy 13 means that the person has 3 copies of chromosome 13 instead of 2.
What is mosaic Trisomy 18?
About 1 in 20 babies might have the extra chromosome 18 in some, but not all, of their cells. This is called mosaic Trisomy 18 (mosaic Edwards’ syndrome). This genetic condition might have lesser effects for many babies; the effects are determined by the type and number of cells that have the extra chromosome.
What is partial Trisomy 18?
About 1 in 100 babies born with partial Edwards’ syndrome (Trisomy 18) have only a portion of the extra chromosome in their cells, rather than the entire extra chromosome. The partial triplicate often results from a balanced translocation of genes carried by one of the parents.
Edwards’ syndrome signs and symptoms
The diagnosis of Edwards’ syndrome must be completed by a medical professional, antenatally, through screening tests. As mentioned earlier, this is done via NIPT (non-invasive prenatal testing), ultrasound, a small blood sample, and chorionic villus sampling or amniocentesis (a sample of amniotic fluid).
For babies born with Trisomy 18, the signs and symptoms are:
- Low birth weight
- Overlapping fingers
- Congenital disabilities, including heart defects
- A weak cry
- Abnormally shaped head
- Failure to thrive
- Severe intellectual disability
- Severe developmental delays
- Small jaw
- Drooping or folded upper eyelid or wider space between eyes.
There might also be episodes of no breathing. The baby’s ears are set lower, the fists are clenched, with a single line on the palm, and the underfoot is convex.
You might be interested to read more in What is Trisomy 18? – Trisomy 18 Foundation
What are the risk factors for Trisomy 18?
Trisomy 18 is not preventable. If it happens, it is not your fault; there’s nothing that you have done to cause this genetic condition. Knowing whether you might be at an increased risk will help with early detection.
A risk factor is advanced maternal age; some association has also been seen with advanced paternal age.
How was Edward’s syndrome discovered?
In 1960, John Hilton Edwards researched newborns with a range of congenital health problems involving developmental delays. He noted Trisomy 18 in the body’s cells; it affected nearly every organ system.
Edwards’ syndrome (Trisomy 18) is now detected by ultrasound by measuring the thickness of the nuchal fold and the absence of the nasal bone.
Is Edward’s syndrome a mutation?
Edwards’ syndrome is a mutation, as there are three copies of chromosome 18 rather than two. The cell division causes the mutation to occur spontaneously at fertilization.
Can a baby with Edward’s syndrome survive?
Babies born with Edwards’ syndrome will not usually survive past one year of age. If diagnosed with mosaic or partial Trisomy 18, life expectancy is increased. However, all forms of the condition come with some delayed fetal development that will affect many children born with this extra chromosome.
Support networks in Australia can be found at Programs — SOFT Australia
Is there a way to prevent Trisomy 18?
Unfortunately, there is no way to prevent trisomy 18. If you have the results of genetic testing information and they are positive for Trisomy 18, you should consult a genetic counselor and be linked with social support networks.
Will Edward’s syndrome affect how I birth?
Every baby’s birth is different. Your health care provider will work with you and your family to prepare you for the birth. Together, you can make a plan for after the birth and discuss any medical interventions that might be necessary, depending on the baby’s medical condition.