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Trisomy 18


What is trisomy 18?

Trisomy 18 is a condition caused by an extra copy of chromosome 18. Chromosomes provide the genetic instructions that program the body to form, grow and develop. Having an extra copy of chromosome 18 causes the body to form differently. 


What are the challenges with trisomy 18?

The most common differences seen in individuals with trisomy 18 are poor growth, heart anomalies, brain anomalies, eye anomalies, cleft lip, cleft palate, kidney anomalies and problems with the digestive system. In addition to physical differences, the body also works differently. Breathing problems, feeding difficulties and developmental disabilities are common. Most babies with trisomy 18 are not able to overcome the challenges and pass away in the first few weeks or months of life.

What causes trisomy 18?

Trisomy 18 is caused by and extra chromosome 18 being present in either the egg or sperm that made the baby. This condition occurs sporadically, meaning parents cannot cause it to happen. Trisomy 18 does not typically run in families. Occasionally, one parent may have a chromosome rearrangement that increases the chance of having children with chromosome differences. It is important that a chromosome analysis be completed to ensure accurate recurrence risk information is shared with the family. 

How common is trisomy 18?

Trisomy 18 is seen in approximately 1 in 5,000 live-born infants.

How is trisomy 18 diagnosed?

Trisomy 18 is diagnosed by a chromosome analysis, also called a karyotype. This test can be done during the pregnancy or after birth. During the pregnancy an amniocentesis procedure removes some fluid from the sac surrounding the baby. A chromosome analysis can be completed on the fluid. After birth, a small blood sample is obtained from the baby for a chromosome analysis. It takes two weeks to get results from a chromosome analysis. Often a preliminary test called FISH can be completed in two days for a rapid result. 

There is a blood test available during pregnancy that screens for trisomy 18. This screen helps determine if the fetus has a high chance or low chance of having trisomy 18. The blood test during pregnancy does not diagnose trisomy 18.


What is the treatment for trisomy 18?

There is not a cure for trisomy 18. Treatment is focused on the individual’s medical needs. Most babies with trisomy 18 die in the first few days or weeks of life, even with invasive medical interventions. The health care team and the family should work together to establish goals for the child and ensure that the medical interventions are working towards the goal. 

Who is on the care team?

At Children’s Mercy Hospital, we have a large care team for children who have trisomy 18. Our Fetal Health Center provides comprehensive care for families expecting a baby with trisomy 18. Our multidisciplinary team works with families to prepare for the birth of the child. Our goal is to provide multiple layers of support to ensure that each family has the best possible experience. Below is a list of teams most commonly involved in the care of children with trisomy 18.   

  • Maternal Fetal Medicine Specialists, high risk OB doctor
  • Ultrasonographers
  • Genetic Counselor
  • Palliative Care team
  • Neonatology
  • Cardiology
  • Surgeon
  • Social Workers
  • Child Life Specialists
  • Chaplains