Edwards' Syndrome (Trisomy 18)

Edwards syndrome, also known as trisomy 18, is a genetic condition caused by the presence of an extra copy of chromosome 18 in some or all of the body’s cells. This additional genetic material significantly disrupts normal development, leading to multiple birth defects, severe intellectual disability, and growth problems. The condition affects multiple organ systems including the heart, kidneys, digestive system, and brain.

Most cases of Edwards syndrome result from complete trisomy 18, where every cell contains three copies of chromosome 18 instead of the usual two. Less commonly, the condition can occur in partial or mosaic forms, where only some cells are affected or only part of the extra chromosome is present.

Edwards syndrome is typically caused by a random error during cell division that occurs when egg or sperm cells are forming. This error, called nondisjunction, results in reproductive cells containing an extra copy of chromosome 18. When fertilisation occurs with these affected cells, the resulting embryo has three copies of chromosome 18 instead of the normal two copies.

The vast majority of Edwards syndrome cases are not inherited and occur randomly in families with no previous history of the condition. While maternal age is associated with increased risk, Edwards syndrome can occur in pregnancies to mothers of any age, and nothing the parents did before or during pregnancy causes the condition.

Edwards syndrome can be detected through various screening and diagnostic methods during pregnancy. Initial screening typically includes first-trimester combined testing with blood tests and nuchal translucency measurement, or second-trimester screening tests. Advanced screening options like NIPT can detect Edwards syndrome from 10 weeks of pregnancy with high accuracy.

Definitive diagnosis requires invasive testing such as chorionic villus sampling (CVS) or amniocentesis, which analyse fetal chromosomes directly. Ultrasound scanning throughout pregnancy can identify physical features associated with Edwards syndrome, including growth restriction, heart defects, and characteristic hand positioning.

Babies with Edwards syndrome typically exhibit severe growth restriction both before and after birth, along with multiple physical abnormalities affecting various organ systems. Common features include complex heart defects, kidney abnormalities, feeding difficulties, and characteristic facial features such as a small head and jaw. Hand positioning with overlapping fingers is frequently observed.

Developmental delays are significant in Edwards syndrome, with affected children experiencing severe intellectual disability and delayed motor skills. Many babies with Edwards syndrome also have breathing difficulties, digestive problems, and increased susceptibility to infections due to the multiple system involvement.

In the vast majority of cases, Edwards syndrome is not inherited and occurs as a random event during egg or sperm formation. Most families affected by Edwards syndrome have no previous family history of chromosomal conditions, and the risk of recurrence in future pregnancies is generally low, slightly above the age-related risk.

Rarely, Edwards syndrome can result from a chromosomal translocation carried by one parent, which may increase the risk of having another affected pregnancy. Genetic counselling can help determine if there are any inherited factors and provide accurate recurrence risk estimates for future pregnancies.

Unfortunately, Edwards syndrome has a poor prognosis, with many affected pregnancies ending in miscarriage or stillbirth. Of babies born with Edwards syndrome, most have significant medical complications that affect survival, with many infants not surviving beyond their first year of life due to the severity of multiple organ system involvement.

However, some children with mosaic or partial forms of Edwards syndrome may have a better prognosis and can survive longer with appropriate medical care. Each case is unique, and families should discuss individual circumstances and care options with their healthcare team and genetic counsellor.

There is no cure for Edwards syndrome, as it is a chromosomal condition affecting every cell in the body. Treatment focuses on managing symptoms and providing supportive care to improve quality of life. This may include surgical interventions for heart defects, feeding support through tubes, breathing assistance, and management of other medical complications.

Care for babies with Edwards syndrome typically requires a multidisciplinary team approach involving paediatricians, cardiologists, nutritionists, and other specialists. The focus is on comfort care and addressing immediate medical needs while supporting the family throughout their journey.

Non-invasive prenatal testing (NIPT) is highly accurate for detecting Edwards syndrome, with high detection rates and low false-positive rates. NIPT screening analyses fetal DNA circulating in the mother’s blood and can be performed from 10 weeks of pregnancy, making it an excellent screening option for many families.

While NIPT is highly accurate, it is still a screening test rather than a diagnostic test. Positive NIPT results typically require confirmation through diagnostic testing such as amniocentesis to provide definitive results before making important pregnancy decisions. Because Edwards syndrome is rare, a substantial proportion of 'higher-chance' NIPT results are not confirmed on diagnostic testing, so a positive screen indicates an increased chance rather than a diagnosis and must always be confirmed before any decisions are made.

Genetic counselling sessions provide comprehensive information about Edwards syndrome, including the condition’s characteristics, inheritance patterns, and implications for current and future pregnancies. Genetic counsellors help families understand screening and diagnostic test results, discuss available options, and provide emotional support throughout the decision-making process.

Genetic counsellors also address questions about recurrence risks for future pregnancies and discuss available screening and diagnostic options. Sessions can be tailored to individual family needs and are available through online genetic counselling services for convenience.

Screening for Edwards syndrome is routinely offered to all pregnant women as part of standard antenatal care, typically through first-trimester combined screening or second-trimester screening tests. Advanced maternal age increases the risk, but screening is appropriate for women of all ages as the condition can occur in any pregnancy.

Additional screening may be particularly important for families with concerning ultrasound findings or those who have had a previous pregnancy affected by chromosomal abnormalities. Detailed anomaly scanning can help identify features that may warrant additional genetic testing.

Comprehensive support is available through healthcare teams, genetic counsellors, and specialised organisations such as SOFT UK (Support Organisation for Trisomy 13/18), which provides resources and connections with other affected families. Many families benefit from counselling services and support groups that understand the unique challenges of Edwards syndrome.

Healthcare support includes coordination between specialists, assistance with care planning, and guidance on available resources. Healthcare teams work closely with families to ensure they have access to appropriate medical care and emotional support throughout their journey.

The risk of Edwards syndrome increases with maternal age, particularly for women over 35 years. However, because younger women have more babies overall, Edwards syndrome can and does occur in pregnancies to mothers of all ages. The increased risk with age is related to changes in cell division that become more common as women get older.

While advanced maternal age is a risk factor, it’s important to remember that the majority of pregnancies to older mothers result in healthy babies. Age-related risk should be considered alongside other factors when discussing screening and diagnostic options during pregnancy.

Ultrasound scanning can identify many features associated with Edwards syndrome, including growth restriction, heart defects, characteristic hand positioning, and various structural abnormalities. However, not all features may be visible on ultrasound, and some findings can be subtle, particularly in early pregnancy.

Detailed anomaly scanning can detect many of the physical features associated with Edwards syndrome. When concerning findings are identified, additional testing such as NIPT or diagnostic procedures may be recommended to clarify the diagnosis.

Complete Edwards syndrome (full trisomy 18) occurs when every cell in the body contains three copies of chromosome 18, resulting in the most severe form of the condition with typical features and poor prognosis. This accounts for approximately 95% of Edwards syndrome cases and is associated with significant developmental delays and multiple organ system involvement.

Partial Edwards syndrome occurs when only part of an extra chromosome 18 is present, while mosaic Edwards syndrome involves only some cells containing the extra chromosome. These rarer forms may have variable presentations and potentially better outcomes, though significant disabilities typically remain present.

Edwards syndrome is specifically caused by an extra copy of chromosome 18, distinguishing it from other trisomy conditions such as Down syndrome (trisomy 21) or Patau syndrome (trisomy 13). Each chromosomal condition has its own characteristic features, prognosis, and associated medical complications.

While all trisomy conditions share some similarities in terms of developmental delays and multiple system involvement, Edwards syndrome typically has a more severe prognosis than Down syndrome but may be somewhat less severe than Patau syndrome. Each condition requires specific medical management and family support approaches.

Families may face difficult decisions regarding pregnancy management when Edwards syndrome is diagnosed, including whether to continue the pregnancy or consider termination. These deeply personal decisions should be made with comprehensive information from healthcare providers and genetic counsellors, taking into account individual circumstances, values, and beliefs.

For families who continue pregnancies affected by Edwards syndrome, decisions may involve birth planning and neonatal care approaches, including the level of medical intervention desired. Healthcare teams work with families to develop care plans that align with their wishes and provide appropriate support throughout the process.

This page was created using information from the following trusted medical sources:

• Edwards Syndrome (Trisomy 18): Genetic Condition, Symptoms & Outlook
• Edwards syndrome (trisomy 18) — Knowledge Hub
• Screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome – NHS
• Edwards’ syndrome – NHS
• Edwards Syndrome – StatPearls – NCBI Bookshelf