Trisomy 18 (Edwards’ syndrome): a guide

The tri in trisomy stands for three, SOFT UK says. It explains that a baby with trisomy 18 has 47 chromosomes in each cell instead of the usual 46, because there are three copies of all or part of chromosome 18. This affects the baby’s development in the womb.

NHS GeNotes calls Edwards syndrome a life-limiting, multisystem genetic condition that causes severe intellectual disability, a high chance of congenital anomalies and often recognisable physical features such as growth restriction, clenched hands and prominent heels.

SOFT UK says trisomy 18 is the second most common trisomy after Down syndrome and ahead of Patau syndrome. It stresses that the right description is life-limiting, not the outdated phrase not compatible with life, because outcomes do vary.

GeNotes says full trisomy 18 accounts for 94 percent of cases. In mosaic Edwards syndrome, around 1 in 20 cases, some cells have three copies and some have two. A smaller number, around 1 in 100, have partial trisomy 18, where only part of the chromosome is tripled.

The NHS and GeNotes both say mosaic and partial forms tend to have milder features, but GeNotes adds that the prognosis is more unpredictable because severity depends on how many cells and which tissues are affected. SOFT UK makes the same point: milder is not guaranteed, and a baby with the full form is not certain to be more affected.

On an ultrasound scan, GeNotes lists suggestive findings including slow growth, heart anomalies, a strawberry-shaped skull, choroid plexus cysts, clenched hands with overlapping fingers, rocker-bottom feet and a single umbilical artery. None is conclusive alone.

The NHS lists features in newborns including low birth weight, low-set ears, cleft lip or palate, club foot, and problems with the heart, kidneys, spine, breathing or digestion. GeNotes puts heart anomalies at 90 percent of cases. It also lists low muscle tone, feeding difficulties, seizures and severe developmental delay among the neurological signs.

The NHS says everyone with Edwards’ syndrome has some level of learning disability and health challenges, and that, like everyone, people with the condition have their own personalities, likes and dislikes.

The NHS says it is not possible to prevent Edwards’ syndrome and that it is not linked to anything you did before or during pregnancy. The chance of having an affected baby increases as the mother gets older, and there is a small extra chance if a previous pregnancy or baby was affected.

GeNotes says it usually arises spontaneously from an error in cell division, most often in the egg. Recurrence risk is usually low. A minority of families have a translocation, and parental chromosome tests are then essential to work out the risk. A clinical genetics referral can help.

The NHS says Edwards’ syndrome is usually screened for in pregnancy. At 10 to 14 weeks you will be invited to a combined test, which is a blood test and an ultrasound scan. If that is missed, a quadruple blood test can be offered between 14 and 20 weeks. GeNotes says that when the chance is 1 in 150 or higher, further testing is offered.

If screening finds something, a specialist referral follows, with more scans and tests such as non-invasive prenatal testing, amniocentesis or chorionic villus sampling. The NHS says the last two can tell you whether your baby definitely has Edwards’ syndrome. It is your choice whether to have them.

GeNotes also notes that the NHS 20-week scan, offered between 18 and 20 weeks plus 6 days, screens for 11 physical conditions including Edwards syndrome. After birth, a blood sample can give a confirmatory diagnosis if the baby has suggestive features.

There is no cure, but the NHS says treatment and support can help children and adults have the best possible quality of life. A range of professionals draw up a care plan with the family. It may include monitoring and surgery for heart, breathing and digestive problems, physiotherapy, occupational therapy, speech therapy, and pain control and palliative care for severe symptoms.

GeNotes says management is complex and needs sensitive counselling and shared decision making. For some children a palliative approach is chosen, and for others more intensive intervention. Care should be delivered by a multidisciplinary team.

SOFT UK adds that medical intervention can raise the chance of survival, and quotes recent research with survival rates of 13.5 percent at one year and 12.3 percent at five years. Numbers like these come from specific studies and cannot predict any one child.

The NHS lists SOFT UK, which supports people affected by Edwards’ or Patau’s syndrome, Bliss for sick or premature babies, and Antenatal Results and Choices, which has information about screening tests and how you might feel. SOFT UK says its support line is a safe, confidential place for anyone whose pregnancy or child is affected.

GeNotes says that when a diagnosis is made in pregnancy, parents should be counselled about the nature of the condition and the options for continuing or ending the pregnancy. Whatever path is chosen, support should continue.

Antenatal screening, fetal medicine, neonatal intensive care, children’s palliative care and community therapies are NHS services. Private genetic testing is available, but a concerning result normally leads to NHS fetal medicine to confirm and plan care.

If you are considering a private test, ask what it screens for, how reliable it is, and who will support you with the result.