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Trisomy 18
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Trisomy 18

Trisomy 18, also known as Edwards syndrome, is a chromosomal condition that causes severe developmental abnormalities and life-threatening medical issues.

Overview

Trisomy 18, also called Edwards syndrome, is a chromosomal condition associated with abnormalities in many parts of the body. Individuals with trisomy 18 often experience slow growth before birth (intrauterine growth retardation) and low birth weight. They may also have heart defects and other organ abnormalities.

Other characteristic features include:

  • A small, abnormally shaped head
  • A small jaw and mouth
  • Clenched fists with overlapping fingers

Due to the presence of several life-threatening medical problems, many individuals with trisomy 18 die before birth or within their first month. Five to 10 percent of children with this condition live past their first year, and these children often have severe intellectual disability.

Frequency

Trisomy 18 occurs in about 1 in 5,000 live-born infants. It is more common in pregnancy, but many affected fetuses do not survive to term. While women of all ages can have a child with trisomy 18, the risk increases as a woman gets older.

Causes

Most cases of trisomy 18 result from having three copies of chromosome 18 in each cell of the body instead of the usual two. This extra genetic material disrupts the normal course of development.

Variations of the condition include:

  • Mosaic trisomy 18: Occurs when an extra copy of chromosome 18 is present in only some of the body's cells. The severity depends on the type and number of cells affected.
  • Partial trisomy 18: Occurs when only part of the long (q) arm of chromosome 18 is present in three copies. Physical signs may be less severe if only a portion of the arm is duplicated.

Chromosome Associated with Trisomy 18

  • Chromosome 18

Inheritance

Most cases of trisomy 18 are not inherited but occur as random events during the formation of eggs and sperm. An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes. Mosaic trisomy 18 is also not inherited and occurs as a random event during early embryonic development.

Partial trisomy 18 can be inherited. An unaffected person may carry a balanced translocation, where genetic material is rearranged between chromosome 18 and another chromosome. While carriers do not show signs of the condition, they are at an increased risk of having children with trisomy 18.

Other Names for This Condition

  • Complete trisomy 18 syndrome
  • Edwards syndrome
  • Trisomy 18 syndrome
  • Trisomy E syndrome

Frequently Asked Questions

Yes. Genetic counseling can help families understand the recurrence risk, which is generally low for non‑mosaic trisomy 18 but higher if a parent carries a balanced translocation involving chromosome 18. Options for future pregnancies include early prenatal testing such as chorionic villus sampling (CVS) or amniocentesis for karyotyping, non‑invasive prenatal testing (NIPT) for screening, and pre‑implantation genetic testing (PGT) if in vitro fertilization is used. Counseling also addresses emotional support and decision‑making around pregnancy continuation.
Newborns with trisomy 18 often have a small, abnormally shaped head (microcephaly), a small jaw (micrognathia), clenched fists with overlapping fingers, low birth weight, and a low-set or malformed ear. Heart defects are common, so a heart murmur or rapid breathing may be noticed early. Parents should also look for a small, flat nose, a cleft palate, and a tendency to have a weak cry or poor feeding. Early detection of these signs can prompt timely evaluation and support.
Because feeding difficulties are frequent, parents should discuss with a neonatologist the possibility of a feeding tube (nasogastric or gastrostomy) and the use of thickened feeds if reflux is an issue. Respiratory support may be needed from the start; this can include continuous positive airway pressure (CPAP) or mechanical ventilation if a heart defect or airway obstruction is present. It is also helpful to have a multidisciplinary team—pediatric cardiology, genetics, nutrition, and palliative care—meet early to plan care goals and anticipate potential complications.
The majority of infants with trisomy 18 die before birth or within the first month of life. About 5–10 % survive beyond the first year, but most of those who do live have severe intellectual disability, limited motor skills, and chronic health problems that require ongoing medical care. Prognosis varies with the presence and severity of heart defects, feeding problems, and other organ involvement.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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