Edwards Syndrome (Trisomy 18)

Edwards syndrome, also called trisomy 18, is a rare chromosomal condition caused by an extra copy of chromosome 18. Because chromosomes carry thousands of genes that guide growth and development, having extra chromosome 18 material can affect many parts of the body, including the heart, brain, kidneys, digestive system and skeleton.

The condition is often detected during pregnancy through screening tests and ultrasound, although some babies are diagnosed after birth when characteristic physical features or medical problems become apparent. The severity can vary considerably, particularly when the extra chromosome is present in only some cells.

Edwards syndrome is a serious condition, and many affected pregnancies end in miscarriage or stillbirth. Among babies born alive, most have significant medical problems and a shortened life expectancy. However, survival is not impossible. A small number of children, particularly those with mosaic or partial trisomy 18, live into childhood, adolescence and, in rare cases, adulthood.

What is Edwards syndrome?

Edwards syndrome occurs when a baby has three copies of chromosome 18 instead of the usual two. This is why it is called trisomy 18.

Most cases are known as full trisomy 18, meaning the extra chromosome is present in essentially all cells. About 5% of people with trisomy 18 have mosaicism, in which some cells have three copies of chromosome 18 while others have the usual two. A much smaller number have partial trisomy 18, where only part of chromosome 18 is present in extra copies.

These different forms matter because they can affect the severity of the condition. Mosaic and partial trisomy 18 can sometimes produce a less severe clinical picture and considerably longer survival.

What is the main cause of Edwards syndrome?

The main cause is an error in chromosome separation called nondisjunction. It usually happens while an egg or sperm cell is being formed. Instead of receiving one copy of chromosome 18, the reproductive cell receives two. After fertilisation, the developing baby therefore has three copies.

This usually happens randomly and is not caused by something a parent ate, did, or failed to do during pregnancy. The risk increases with maternal age, although a baby with trisomy 18 can be conceived at any reproductive age.

Rarely, trisomy 18 results from a chromosomal rearrangement such as a translocation. In these cases, genetic testing of the parents may be recommended because a parent can carry a balanced chromosome rearrangement without having symptoms.

What happens to babies with an extra chromosome?

An extra chromosome does not simply add one small feature to a baby. It changes the amount of genetic information available to developing cells.

The additional chromosome 18 material alters normal development and can affect several organ systems simultaneously. Babies may have restricted growth before birth, congenital heart defects, differences in brain development, kidney abnormalities, feeding difficulties, breathing problems and characteristic changes involving the hands, feet and face.

The effects can be very different from one baby to another. This is one reason a prenatal diagnosis cannot, by itself, predict exactly how a particular child will develop.

What does a child with trisomy 18 look like?

There is no single appearance, but several physical characteristics are commonly associated with Edwards syndrome.

A baby may have:

• Low birth weight and poor growth
• A small head
• A prominent back of the skull
• A small lower jaw
• Low-set ears
• A narrow or unusual facial appearance
• Clenched hands with overlapping fingers
• Clubfeet or rocker-bottom feet
• Short breastbone
• Muscle weakness or contractures

Heart, kidney, brain and gastrointestinal abnormalities may also be present.

The image accompanying this article illustrates several of these commonly described features, including overlapping fingers, rocker-bottom feet and congenital heart and kidney abnormalities.

What are the first signs of trisomy 18?

The first signs are often detected before birth, rather than after delivery.

During an ultrasound, doctors may notice:

• Fetal growth restriction
• Abnormal head or skull shape
• Clenched hands or unusual finger positioning
• Clubfeet
• Congenital heart abnormalities
• Brain or spinal abnormalities
• Certain kidney abnormalities
• Choroid plexus cysts
• Abdominal wall abnormalities
• Excess amniotic fluid in some pregnancies

Not every baby will have all of these findings. Some abnormalities may be subtle, particularly earlier in pregnancy.

After birth, poor feeding, breathing difficulties, low birth weight, unusual hand positioning and congenital heart problems may prompt doctors to investigate further.

Can you detect trisomy 18 on ultrasound?

Yes, ultrasound can identify findings that raise suspicion for trisomy 18, but ultrasound alone cannot definitively diagnose it.

First-trimester ultrasound may identify increased nuchal translucency or other structural abnormalities. The detailed anatomy scan (also known as anomaly scan), usually performed around 18 to 22 weeks, can look for abnormalities involving the brain, heart, abdomen, limbs and other organs.

A blood-based screening test such as cell-free DNA screening can also estimate the likelihood of trisomy 18. However, a screening result is not the same as a diagnosis.

If diagnostic confirmation is needed, tests such as chorionic villus sampling (CVS) or amniocentesis can examine fetal chromosomes directly.

Does trisomy 18 run in families?

Usually, no. Most cases occur because of a random chromosome-separation error and are not inherited from either parent.

There is an important exception. If trisomy 18 results from an unbalanced translocation, one parent may carry a balanced translocation. The parent may be completely healthy but have an increased chance of passing an abnormal chromosome arrangement to a child.

This is why chromosome analysis and genetic counselling can be particularly important after a diagnosis.

What makes you high risk for trisomy 18?

The strongest established risk factor is increasing maternal age. The chance of chromosome nondisjunction increases as eggs age.

Other circumstances that may lead doctors to offer closer evaluation include:

• A previous pregnancy affected by trisomy 18
• A parent carrying a chromosome rearrangement
• An abnormal prenatal screening result
• Ultrasound findings suggestive of trisomy 18
• A family history of a relevant chromosome rearrangement

Importantly, “high risk” does not mean that a baby definitely has trisomy 18. Screening estimates probability; diagnostic testing establishes whether the fetus actually has the chromosomal condition.

Can a child survive Edwards syndrome?

Yes. Some children with Edwards syndrome survive beyond infancy, although the majority of babies with full trisomy 18 have a very high risk of dying during pregnancy, shortly after birth, or within the first year.

MedlinePlus reports that about half of affected infants do not survive beyond the first week and approximately nine out of 10 die by one year, although survival varies depending on the type of trisomy, associated abnormalities and medical care.

Studies of children who survive longer show that survival into childhood and adolescence is possible. A small number of people with mosaic or partial trisomy 18 reach adulthood.

How long does a child with trisomy 18 live?

There is no single life expectancy that applies to every child.

For babies with full trisomy 18, survival is generally short. However, some children survive for years, and exceptional cases have reached adulthood. One population-based study found approximately 12.6% one-year survival and 9.8% ten-year survival among children with trisomy 18 in its study population.

Long-term survival is influenced by factors such as the chromosome pattern, heart defects, respiratory problems, feeding ability, birth weight, gestational age and other medical complications.

Can someone with trisomy 18 live to adulthood?

Yes, although it is rare.

Published medical literature includes adolescents and adults with trisomy 18. Case reports have described people with complete trisomy 18 surviving to 16, 19 and 26 years of age.

There are also reports of much older individuals. A review of the literature cited a reported 50-year-old woman with trisomy 18. Because exceptional cases are uncommon and there is no comprehensive worldwide registry of the oldest survivors, it is safer to describe 50 years as a reported exceptional survival, rather than a universally established maximum lifespan.

People who survive into adulthood generally continue to have significant developmental and medical needs, although the degree of disability can vary, particularly with mosaic trisomy.

Do babies with trisomy 18 feel pain?

A diagnosis of trisomy 18 does not mean a baby cannot feel pain. Babies with the condition can experience discomfort or pain from medical problems such as breathing difficulties, infections, feeding problems, procedures or congenital abnormalities.

At the same time, it is impossible to predict an individual baby’s pain experience simply from the chromosome diagnosis. Medical teams can assess signs of discomfort and provide appropriate comfort measures, including pain relief when needed.

For families facing a prenatal or newborn diagnosis, discussions about symptom control, palliative care and treatment options should be individualised rather than based solely on the diagnosis.

What are the leading causes of death in trisomy 18?

The causes vary according to age and the specific medical problems present.

In newborns, serious cardiopulmonary problems, including congenital heart disease, respiratory failure, pulmonary hypertension and central apnea, are major contributors to mortality. Severe feeding difficulties and aspiration can also contribute to complications.

Among people who survive beyond the first year, infections become an important cause of death. A 2023 study of 174 individuals who survived their first year found that infectious causes were prominent among later deaths, while cardiopulmonary causes predominated in earlier literature concerning infants.

Is trisomy 18 more common in males or females?

Trisomy 18 is more commonly observed in females among live births. MedlinePlus estimates that it occurs about three times as often in girls as boys.

The difference is thought to be partly related to higher fetal loss among male pregnancies affected by trisomy 18.

What are trisomy 13 and trisomy 18?

Trisomy 13, also known as Patau syndrome, occurs when there is extra chromosome 13 material. It can cause severe abnormalities involving the brain, eyes, heart, face, fingers and toes.

Trisomy 18, or Edwards syndrome, involves extra chromosome 18 material and is particularly associated with growth restriction, congenital heart disease, abnormalities of the hands and feet, brain abnormalities and multiple congenital anomalies.

Both conditions are serious chromosomal disorders and have high infant mortality.

What’s the difference between trisomy 13, 18 and 21?

All three are autosomal trisomies, meaning an extra copy of one of the non-sex chromosomes is present.

Trisomy 21 generally has a considerably better survival outlook than trisomy 13 or 18.

What is the deadliest trisomy?

There is no official medical ranking that labels one autosomal trisomy as “the deadliest.”

However, trisomy 13 and trisomy 18 are both among the most severe viable autosomal trisomies, with very high rates of fetal loss and infant mortality. Trisomy 18 has particularly high mortality, although outcomes vary substantially between studies and individual patients.

Trisomy 21 is substantially less lethal and has a very different long-term prognosis.

Do most trisomy 18 babies miscarry?

Many pregnancies affected by trisomy 18 end in miscarriage or stillbirth.

The exact percentage depends on when the pregnancy is diagnosed. In a large study of prenatally diagnosed trisomy 18 pregnancies, researchers estimated substantial fetal loss after diagnosis, with only about 30% of viable fetuses diagnosed at 12 weeks ultimately resulting in a live birth.

Therefore, the phrase “most miscarry” is broadly reasonable when discussing pregnancies affected by trisomy 18, but the exact risk cannot be applied equally to every pregnancy.

What are the chances of having trisomy 18 twice?

For most families whose previous pregnancy involved full trisomy 18 caused by a random nondisjunction event, the recurrence risk is low but not zero.

One clinical reference estimates the recurrence risk for complete trisomy 18 at approximately 0.5% to 1% in a subsequent pregnancy. If a parent carries a balanced translocation associated with partial trisomy 18, the recurrence risk can be substantially higher and depends on the exact chromosome rearrangement.

Anyone who has had a pregnancy or child affected by trisomy 18 should consider genetic counselling before or during a future pregnancy.

Is it possible to have a healthy pregnancy after trisomy 18?

Yes. Having one pregnancy affected by trisomy 18 does not mean that every subsequent pregnancy will be affected.

Because most cases are random chromosome-separation events, most parents go on to have unaffected pregnancies. However, the risk is slightly higher than the background risk, and the individual risk depends on maternal age, the chromosome findings in the affected pregnancy and whether either parent has a chromosome rearrangement.

A genetic counsellor can review the previous child’s or pregnancy’s chromosome report and discuss options for screening and diagnostic testing in a future pregnancy.

Can Edwards syndrome be prevented?

There is currently no proven way to prevent Edwards syndrome.

Because most cases result from random errors during chromosome formation, they are not caused by lifestyle choices, diet, exercise, stress or anything a parent did during pregnancy.

What can be done is early detection and appropriate counselling. Prenatal screening, ultrasound and diagnostic testing can help identify the condition during pregnancy and allow parents and doctors to plan appropriate care.

How is Edwards syndrome diagnosed?

Diagnosis can happen before or after birth.

During pregnancy, screening may include:

• First-trimester ultrasound
• Maternal blood screening
• Cell-free DNA screening
• Detailed fetal ultrasound

A positive screening test does not confirm trisomy 18. Diagnostic testing with CVS or amniocentesis can examine fetal chromosomes and provide confirmation.

After birth, a doctor may suspect Edwards syndrome based on physical features, growth restriction and congenital abnormalities. A karyotype or other chromosome test can then confirm the diagnosis.

How is Edwards syndrome treated?

There is no treatment that removes the extra chromosome 18. Management therefore focuses on the individual baby’s or child’s medical needs.

Depending on the circumstances, care may involve:

• Support for breathing
• Feeding assistance
• Treatment of infections
• Management of seizures
• Cardiology care
• Kidney and urinary evaluation
• Physical and developmental support
• Treatment of gastrointestinal problems
• Surgery for selected congenital abnormalities
• Palliative and comfort-focused care when appropriate

Medical and surgical approaches have evolved, and some children may benefit from interventions that were previously used less often. Decisions should be made individually with the family and a multidisciplinary medical team.

Frequently asked questions about Edwards syndrome

Is Edwards syndrome always fatal?

No. It is a life-limiting condition with a very high mortality rate, particularly in full trisomy 18, but some children survive into childhood and a small number reach adulthood.

Can trisomy 18 be diagnosed during pregnancy?

Yes. Screening and ultrasound can raise suspicion, while CVS or amniocentesis can provide diagnostic confirmation.

Is mosaic trisomy 18 less severe?

It can be. Mosaic trisomy 18 affects only some cells, and the clinical picture can range from relatively mild to severe. The exact effects depend on which cells are affected and how much trisomic tissue is present.

Does maternal age increase the risk?

Yes. The likelihood of trisomy 18 increases with maternal age, although it can occur at any age.

Can a baby with trisomy 18 have a normal ultrasound?

A normal ultrasound cannot completely rule out trisomy 18. Ultrasound can identify many associated abnormalities, but some findings may be subtle or absent. Screening and, when indicated, diagnostic chromosome testing provide additional information.

What should parents do after a trisomy 18 diagnosis?

Parents should receive clear information about the chromosome result, the baby’s specific ultrasound findings and the available care options. Genetic counselling and consultation with maternal-fetal medicine or paediatric specialists can help families understand the diagnosis and make informed decisions.

Final thoughts

Edwards syndrome is a complex genetic condition, and its diagnosis can bring difficult and emotional questions for families. The most important thing to remember is that trisomy 18 does not have exactly the same outcome for every baby.

Full trisomy 18 usually causes severe medical problems and carries a very high risk of death before birth or during infancy. At the same time, mosaic and partial forms can sometimes be less severe, and exceptional long-term survivors have been documented.

If trisomy 18 is suspected during pregnancy, ultrasound findings should be interpreted alongside appropriate genetic screening or diagnostic testing. A diagnosis should also be discussed with a qualified genetic counsellor and specialist medical team so that parents receive an individualised understanding of prognosis, treatment and future pregnancy risks.

To consult a Pediatrician at Sparsh Diagnostic Centre, call our helpline number 9830117733.

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