What Is Trisomy 18?

Trisomy 18 is a serious genetic condition. It is also sometimes called Edward syndrome. It can cause many different symptoms that are most often life-limiting. Not all babies with trisomy 18 will have the same differences or challenges. Some common things that can be caused by trisomy 18 include:

  • Heart problems
  • Kidney problems
  • Clenched hands
  • Slow growth during pregnancy
  • Cleft lip and/or palate

Trisomy 18 also causes challenges after birth, such as:

  • Breathing problems
  • Severe intellectual disability
  • Feeding problems
  • Seizures
  • Hearing problems

What Causes Trisomy 18?

Most people have two copies of each chromosome. Our chromosomes hold all our genetic information. Trisomy 18 happens when there is an extra copy of chromosome 18 in either the egg or the sperm before conception. This means that the baby will have three copies of chromosome 18 instead of two. The extra chromosome can cause differences in the way a baby develops. Most often, trisomy 18 happens by chance. It is not caused by anything you did or did not do during your pregnancy.

How Common Is Trisomy 18?

Trisomy 18 happens in about one in 3,300 pregnancies in the United States. The risk for trisomy 18 goes up as a mother gets older, but any woman at any age can have a baby with trisomy 18.

Are There Different Types of Trisomy 18?

Most of the time, a baby with trisomy 18 has the extra copy of chromosome 18 in all the cells in their body. Less commonly, some cells have the extra copy of chromosome 18 but some do not. When this happens, it is called “mosaic trisomy 18”. People with mosaic trisomy 18 might have milder symptoms.

How Is Trisomy 18 Diagnosed?

Most babies with trisomy 18 will have abnormal ultrasound findings during pregnancy. These findings might be seen in the first trimester, but they are more commonly seen during a second trimester ultrasound.

There are also genetic tests for trisomy 18 during pregnancy. Some tests, called “screening tests”, can be done using a sample of the mother’s blood to determine if there is a high risk for trisomy 18 in the baby. These screening tests cannot diagnose or rule out trisomy 18 for sure. The way to get a more definite answer about trisomy 18 is with “diagnostic” genetic testing. Diagnostic genetic testing for trisomy 18 can be done by testing the placenta (called a “chorionic villi sample” or CVS) during the first trimester of pregnancy or the amniotic fluid (called an “amniocentesis”) during the second or third trimesters. These tests pose a small risk for miscarriage or preterm labor, most often less than one in 500 (0.2%).

Some people may have genetic testing as part of their normal pregnancy care and a high-risk or diagnostic result for trisomy 18 may be unexpected. Other people may have genetic testing after abnormal ultrasound findings raised the concern for trisomy 18 to get more certain answers about the diagnosis.

What Are the Treatment or Intervention Options?

There are no treatments or cures for the extra chromosome that causes trisomy 18. Treatment for babies and children with trisomy 18 is focused on the symptoms they have. There have been recent studies to see if there are treatments that can improve the quality or length of the lives of babies with trisomy 18. Even with these treatments, children with trisomy 18 will not grow and learn the same way as other children and they will have a shortened lifespan.

After learning about the diagnosis of trisomy 18, families can choose to continue or to end their pregnancy. These decisions are personal and each family’s decision is unique. Both are decisions made by loving parents. For those who continue the pregnancy, parents often consider what “quality of life” means to them and what treatment options would best support this. Some of these treatments might include surgeries, medicines, breathing machines, and feeding tubes. But the symptoms and treatments might be difficult. Some families choose to focus on treatments that will keep the baby comfortable, instead of treatments to extend their life. This is called “comfort care”.

What Is the Long-term Outlook?

Unfortunately, trisomy 18 is often a severe condition and most babies with it do not survive to their first birthday. However, some babies with trisomy 18 have milder symptoms and can survive longer. For babies who survive longer, they usually need frequent visits to their primary care and specialist doctors. They may need frequent hospital stays, surgeries, or other medical treatments.

All babies with trisomy 18 have developmental delays and intellectual disability; they may not learn how to do things that typical children do, such as walk and talk. Children with trisomy 18 will require special care for their entire lives.