What Is Trisomy 18 or Edwards Syndrome?

Trisomy 18 is a rare genetic disorder that affects approximately 1 in every 3,315 births in the United States — around 1,187 babies each year.

In typical development, a baby gets 23 pairs of chromosomes from its parents during conception — 22 are called autosomes, and 1 set is made up of sex chromosomes (X and/or Y, depending on the baby’s sex).

The word “trisomy” means three bodies. When there are three copies of the chromosome versus the usual two, it creates an imbalance. As a result, a baby may be born with certain structural changes some of which may lead to miscarriage, stillbirth, or death after the baby is born.

Variations

Babies can be born with an extra copy of chromosome 18 in each cell in the body. This is called complete trisomy 18 and causes more serious health outcomes.

Mosaic trisomy 18 happens when only some cells in the body contain the extra chromosome. Around 5 percent of babies with trisomy 18 have the mosaic form. This generally leads to milder irregularities and longer life expectancy.

Partial trisomy 18 happens when an extra copy of chromosome 18 attaches to another chromosome. Again, the severity of the syndrome tends to be associated with the total number of cells affected by the trisomy. So, a partial trisomy tends to have less severe effects and longer life expectancy.

You may not notice anything different in your pregnancy if your baby has Edwards syndrome. In fact, you may not learn about your baby’s diagnosis until after your doctor orders certain prenatal screening tests, like:

• cell-free DNA screening
• ultrasound
• amniocentesis

Some families do not discover their child’s diagnosis until birth, when the following physical features may include:

• low birth weight
• low muscle tone
• smaller head
• wide-set eyes
• small lower jaw
• cleft lip or palate
• webbed neck
• hand issues, like clenched first or second and fifth fingers on top of other fingers
• rocker bottom feet
• crossed legs
• shortened breastbone

Other health issues may include:

• feeding or sucking difficulties
• trouble gaining weight (also known as failure to thrive)
• congenital heart issues, like ventricular septal defect
• cryptorchidism — undescended testicles
• eye or vision issues, like clouding of the corneas, small eyes, strabismus (crossed eyes), or nystagmus (uncontrolled eye movements)
• hearing loss
• seizures
• gastrointestinal issues
• cancerous tumors, particularly in the kidneys and liver

Trisomy 18 is caused by any situation that leads to an extra copy of chromosome 18 in the body.

In most cases, it happens when the sperm meets the egg during conception. In one scenario, the reproductive material of either parent may spontaneously divide. In another, the trisomy may happen as cells divide after fertilization. Whatever the case, the extra chromosome happens at random.

Translocation is another possibility, which means that parts of chromosomes break off and attach to other chromosomes. This may happen randomly or through a “balanced” translocation, in which one parent has a set of chromosomes that aren’t typical but are balanced. When chromosomes are balanced, they don’t cause medical issues. After reproduction, though, genetic information passed on may cause a trisomy.

Edwards syndrome may be diagnosed at some point during your pregnancy. You may have a cell-free DNA screening (cfDNA) at any time after 10 weeks of pregnancy and until delivery. cfDNA is a simple blood test that screens for genetic conditions. A positive result on this test means you’ll need further testing to confirm the results.

Other tests during pregnancy include:

• Amniocentesis and chorionic villus sampling are more invasive diagnostic tools you may get after 15 weeks of pregnancy. Your doctor will take a sample of your amniotic fluid or placenta to look for extra copies of chromosome 18.
• An ultrasound exam may uncover physical features (small head, webbed neck, hand or foot irregularities, etc.) of the syndrome.

Other times, trisomy 18 may not be diagnosed until after your baby is born. Your child’s doctor may diagnose it based on:

• physical features or characteristics
• heart issues or other defects
• blood tests that analyze your child’s chromosomes

There is no cure for trisomy 18. Since babies with this condition tend to have multiple health issues, you’ll work with a team of doctors to create a customized treatment plan. In more severe cases, some families favor palliative care or hospice care.

Treatments are more about making a child comfortable or correcting the issues that affect an individual child. For example, surgery may be an option to treat things like:

• heart defects
• kidney issues
• head or face irregularities

As a child grows, they may need support academically and physically. Early intervention and special education programs can help fill these gaps.

You may be surprised to learn that there are very few risk factors for Edwards syndrome.

There may be an increased chance of having a baby with a trisomy as you get older. While different reports show mothers in their late teens and 20s can have children with trisomy 18, the mean age is closer to 32.5 years old.

In rare cases, trisomy 18 may be inherited from a biological parent (through balanced translocation). If you already have had one child with a trisomy, your doctor may suggest getting genetic testing to assess your chances of having another child with a similar condition.

The vast majority of the time, though, Edwards syndrome happens by chance during conception when the sperm meets the egg.

It’s important to be prepared for all possibilities with a condition like trisomy 18. Researchers share that nearly half of all babies born with Edwards syndrome who survive delivery may not live beyond the first week of life.

That said, the severity of the syndrome depends on the type (complete, mosaic, partial, etc.) and whatever effects it has on your individual child. All children are different, and all outlooks will be unique as a result.

Of children born with Edwards syndrome, nearly 50 percent will not survive beyond the first week of life. However, around 10 percent will reach their first birthday, and some may live to their teen years or even adulthood, but they will need medical support or therapies, including:

• physical therapy
• occupational therapy
• speech therapy

While you may be worried about your child and the outlook over the long term, try taking it day by day. And don’t forget about yourself or your own mental health in the process.

There is support for families with children who have Edwards syndrome. Consider contacting the Trisomy 18 Foundation or the Support Organization for Trisomy 13, 18, and Related Disorders (SOFT). Your doctor may also be able to help connect you with a local group for support and other resources.