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Trisomy 18

(Edwards Syndrome; Trisomy E)


Nina N. Powell-Hamilton

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Reviewed/Revised Dec 2021 | Modified Sep 2022
Topic Resources

Trisomy 18 is a chromosomal disorder caused by an extra chromosome 18 that results in intellectual disability and physical abnormalities.

  • Trisomy 18 caused by an extra chromosome 18.

  • Infants are typically small and have many physical abnormalities and problems with internal organs.

  • Tests can be done before or after birth to confirm the diagnosis.

  • There is no treatment available for trisomy 18.

An extra chromosome, making three of a kind (instead of the normal two), is called trisomy ( see also Overview of Chromosome and Gene Disorders Overview of Chromosome and Gene Disorders Chromosomes are structures within cells that contain a person's genes. A gene is a segment of deoxyribonucleic acid ( DNA) and contains the code for a specific protein that functions in one... read more ). Children who have trisomy 18 have a third chromosome 18. Trisomy 18 occurs in about 1 out of 6,000 live births. However, many affected fetuses spontaneously miscarry Miscarriage A miscarriage is the loss of a fetus before 20 weeks of pregnancy. Miscarriages may occur because of a problem in the fetus (such as a genetic disorder or birth defect) or in the woman (such... read more . The extra chromosome almost always comes from the mother. Mothers who are over age 35 are at increased risk of having a child with trisomy 18. There are more girls than boys with trisomy 18.

Symptoms of Trisomy 18

In the womb, affected fetuses are not typically very active, and there is often excess amniotic fluid and a small placenta.

Physical abnormalities

At birth, newborns are often very small because their muscles and body fat are underdeveloped. Newborns are typically limp and have a weak cry. The mouth and jaw may be small, which gives the newborn's face a pinched appearance. Other visible deformities are common, including a small head, low-set and malformed ears, a narrow pelvis, and a short breastbone (sternum). Physical abnormalities may be obvious at birth. However, some newborns have abnormalities that are not as severe.

Common Types of Clubfoot

Common Types of Clubfoot

The hands are clenched in fists, and the index fingers often overlap the middle and ring fingers. The fingernails are underdeveloped. Skinfolds, especially over the back of the neck, are common. The big toes are shortened and frequently bend upward. Clubfeet Clubfoot and Other Foot Defects Clubfoot (talipes equinovarus) is a birth defect in which the foot and ankle are twisted out of shape or position. Birth defects, also called congenital anomalies, are physical abnormalities... read more Clubfoot and Other Foot Defects and rocker-bottom feet are common.

Physical Abnormalities in Trisomy 18

Internal abnormalities

Diagnosis of Trisomy 18

  • Before birth, ultrasonography of the fetus or blood tests of the mother

  • Chorionic villus sampling, amniocentesis, or both

  • After birth, the appearance of the infant and blood tests of the infant

After birth, the infant's physical appearance may suggest the diagnosis of trisomy 18. To confirm the diagnosis of trisomy 18, the infant's chromosomes typically are analyzed using a blood test.

Prognosis for and Treatment of Trisomy 18

  • Support for the family

There is no specific treatment available for trisomy 18. About 50% of children die within the first week, and only 5 to 10% are still alive at 1 year of age. However, recently, people who have trisomy 18 are living longer, and there are adults with trisomy 18. These survivors are at increased risk of developing certain tumors, such as in the liver (hepatoblastoma Hepatoblastoma Primary liver cancers are cancers that originate in the liver. The most common is hepatocellular carcinoma (hepatoma). At first, liver cancer usually causes only vague symptoms (such as weight... read more ) and kidneys (Wilms tumor Wilms Tumor Wilms tumor is a specific kind of kidney cancer that occurs mainly in young children. The cause of Wilms tumor is not known, but some children may have a genetic abnormality that increases their... read more ). To help detect these tumors and other complications, doctors may recommend that children have periodic blood tests and imaging studies such as ultrasonography of the abdomen and kidneys.

Children who survive have severe developmental delay and disability. It is recommended that family members seek support.

More Information

The following are English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

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