What is Edwards Syndrome (Trisomy 18)?

Trisomy 18 Is More Common In Girls

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One of the more serious health conditions checked in routine prenatal diagnostic screening is Edwards Syndrome, a chromosomal condition with a devastating prognosis. Edwards Syndrome is also known as Trisomy 18 Syndrome because there are three copies of chromosome 18.

Edwards Syndrome Statistics

Edwards Syndrome occurs in 1 out of every 6,000 live births and is three times more common in girls, according to the National Institutes of Health (NIH).

However, the incidence during pregnancy is much higher because as many as 95 percent of women whose fetus has trisomy 18 have a miscarriage or stillbirth

Prognosis for Babies with Edwards Syndrome

Sadly, the NIH explains the outcomes for babies born with Edwards Syndrome are not good, including:

  • Half of infants do not survive beyond the first week of life.
  • Nine out of 10 children will die before their first birthday. 
  • Some children survive to the teenage years, but with serious medical and developmental problems.

Types of Edward's Syndrome

The most common form of Edwards Syndrome is full trisomy 18, meaning the baby has three full copies of the 18th chromosome instead of two.

It is also possible to have partial trisomy 18, in which there are two full copies of chromosome 18 and also an additional partial copy.

Still another type is mosaic trisomy 18, meaning there is an effect on some, but not all, cells.

The latter two types are rare compared to full trisomy 18. The prognosis does not differ by type.

Causes and Risk Factors of Edward's Syndrome

The extra copy of chromosome 18 is already present at the time of fertilization and results from random errors in cell division. Trisomy 18 can occur in parents of all age groups, but the risk is highest when moms are older than 35.

Edward's Syndrome Diagnosis

An amniocentesis or chorionic villus sampling can test for Edward's Syndrome. The alphafetoprotein test cannot confirm (or entirely rule out) trisomy 18 but can merely indicate statistical odds that the baby might have the condition. Some tests are less accurate than others.

Genetic testing is an evolving field and, surely, newer and more accurate tests are on the horizon.

Risk of Recurrence for Edward's Syndrome

Most of the time, trisomy 18 is a random occurrence due to problems in cell division. In rare cases, parents are carriers for partial trisomy 18 due to a condition called balanced translocation that increases the risk for future pregnancies.

If there is a chance you might be a carrier, your doctor can refer you to a genetic counselor to discuss your options. But most parents who have babies with trisomy 18 are not carriers.

Facing an Edwards Syndrome Diagnosis

An Edwards Syndrome diagnosis is devastating news. Many parents choose to terminate their pregnancies after receiving a confirmation that the baby definitely has trisomy 18, given the high risk of severe health problems and the low odds of the baby surviving infancy.

Others decide to continue the pregnancy anyway, either because of beliefs against abortion or because of a mindset that they want to treasure the time with the baby even if it is short.

There is no "correct" choice for what to do in this situation. Parents facing this diagnosis should do what feels right for them.

Sources:

Medline Plus: Trisomy 18 (2016) 

Trisomy 18 Foundation: What Is Trisomy 18?

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