Trisomy 18

Trisomy 18

If you have just found out through prenatal testing that your baby has Trisomy 18 or may have Trisomy 18 and are looking for more information, Genetic Support Foundation is a good starting point.

There are other important resources out there, including your doctor and genetic counselor. We have also compiled a list of resources that can provide you with additional information and support.

After reviewing the information below, if you have a question that you are having difficulty finding an answer for, please feel free to contact us.

Overview of important information about Trisomy 18

Trisomy 18, also called Edwards syndrome, is a chromosomal condition that occurs in approximately 1 in 5,000 live-born babies (it is more common than this, but many babies with Trisomy 18 miscarry during the pregnancy).  Trisomy 18 is the result of the baby having 3 copies of chromosome 18 instead of the typical two copies.  This extra chromosome causes the intellectual and physical problems associated with Trisomy 18.  Most babies who are born with this condition pass away shortly after birth or within the first year of life, however, some can live longer.

There is nothing that mom or dad can do to cause or prevent Trisomy 18.  This is a condition that does increase in risk as mom’s age increases, however, women of all ages can have a baby with Trisomy 18.

Most cases of Trisomy 18 involve the individual having an extra copy of chromosome 18 in all of the cells of their body.  However, there are a couple of other types of Trisomy 18:

  • Mosaic Trisomy 18– In this situation only some of the cells (not all) in the body having an extra chromosome 18.
  • Partial Trisomy 18– This can occur if mom or dad carries a rearrangement of their chromosomes that involves chromosome 18. The baby can end up having 3 copies of part of chromosome 18 but not all of chromosome 18, which is why it is called partial Trisomy 18.

Both mosaic Trisomy 18 and partial Trisomy 18 may be mild or severe, depending on how many and which cells have the extra 18 in mosaic Trisomy 18 and how much of the chromosome 18 is in extra in partial Trisomy 18.

What causes Trisomy 18?

Trisomy 18 is the result of the baby having an extra chromosome 18 (instead of having 2 they have 3 chromosome 18s).

As humans, we typically have 23 pairs of chromosomes in each of our cells or a total of 46 chromosomes. Individuals with Edwards syndrome or Trisomy 18 have an extra copy of the material from chromosome #18. In most cases, this is due to a whole extra copy of chromosome #18, which is called Trisomy 18. This increases in incidence as mom ages. This extra genetic material from chromosome 18 is the reason that individuals with this condition typically have severe intellectual disability and an increased risk for other birth defects and health concerns.

Trisomy 18 cannot be cured. Most cases of Trisomy 18 are sporadic, meaning it does not run in families With sporadic Trisomy 18, it is unlikely that if you have one child with it that future children would also have it, although the likelihood of this increases slightly above your age related chance. There are some cases of partial Trisomy 18 that can run in the family (when caused by a rearrangement in mom or dad’s chromosomes), but it is rare for this to happen. In the type that runs in the family, recurrence risk or chance of future children having Trisomy 18 is higher. A picture of the baby’s chromosomes (karyotype) can determine if it is the type that is sporadic  or the type that runs in the family.

Is there anything I can do to cause or prevent Trisomy 18?

Based on current research, there is nothing that mom or dad can do to cause or prevent Trisomy 18.  This is a condition where chances increase as mom’s age increases. However, women of all ages can have a baby with Trisomy 18.

What are some common things seen on prenatal ultrasound in babies with Trisomy 18?

Examples of things that are seen more frequently on ultrasound during pregnancy in babies that have Trisomy 18 include heart defects and clenched hands, among other things.  These things can also be seen in babies without Ttrisomy 18, so for definitive information regarding Trisomy 18 during the pregnancy, amniocentesis or CVS is recommended.

What is the long term outcome for individuals with Trisomy 18?

Due to the fact that Trisomy 18 is associated with severe intellectual disability and physical abnormalities, many babies with Trisomy 18 miscarry, are stillborn or die before birth or within the first month of life. Typically, up to 10% of children with Trisomy 18 can live past their first year.

Individuals with mosaic Trisomy 18 (meaning only some of their cells have an extra chromosome 18) may have a less severe long term outcome than those with full Trisomy 18.  It is difficult to predict outcome prior to seeing how the baby develops over time.

Individuals with partial Trisomy 18 (part of their chromosome 18 is in extra but not the whole chromosome) may have a long term outcome much different and possibly less severe than full Trisomy 18.

How does having a baby with Trisomy 18 affect a family?

Data to answer this question is limited, however, this is an excerpt pulled from a study done in 2012 titled, The Experience of Families with Children with Trisomy 13 and 18 in Social Networks1.

“Although most parents described their children as having significant neurodevelopmental disabilities, almost all parents reported a positive view of family life and the quality of life of their child with Trisomy 13 or Trisomy 18. These parents overwhelmingly described surviving children as happy and stated that they were able to communicate with them to understand their needs. Parents seemed to accept their children’s limitations and to celebrate their small achievements. When children died, parents viewed their short lives as being valuable. Yet at the same time, parents acknowledged that there were significant financial sacrifices and that their children experienced more pain than other children. Most parents reported that their family was strengthened since the birth, and often the death, of a child with Trisomy 13 or Trisomy 18.” 1

What are my options if Trisomy 18 is diagnosed during pregnancy?

Please see our section on receiving a prenatal diagnosis for more information about your options.  This is a difficult time and you are not alone.  If there is anything we can do to help you, please contact us.


Other Resources

Trisomy 18 Foundation

Genetics Home Reference– Trisomy 18


1. Janvier, A, Farlow B, Wilfond, BS. 2012. The Experience of Families with Children with Trisomy 13 and 18 in Social Networks. Pediatrics 130(2):293-8.

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