Trisomy 18Definition: Trisomy 18 is a syndrome associated with the presence of a third (extra) number 18 chromosome.
Alternative Names: Edwards syndrome
Causes, incidence, and risk factors: Trisomy 18 is a relatively common syndrome affecting approximately 1 out of 3,000 live births, and affecting girls more than three times as often as boys. It is caused by the presence of an extra number 18 chromosome, which leads to multiple abnormalities. Many of these abnormalities make it hard for infants to live longer than a few months.
Signs and tests: Examination of the pregnant woman may show polyhydramnios (extra amniotic fluid). At the birth of the child, an unusually small placenta may be noted. Physical examination may show an excess of arched type finger print patterns. X-rays may reveal a short breast bone (sternum). Chromosome studies show trisomy 18, partial trisomy, or translocation.
Treatment: Life-sustaining measures are not recommended.
Support Groups: Contact the following organizations for more information:
Expectations (prognosis): The abnormalities of trisomy 18 are generally not compatible with more than a few months of life. Fifty percent of the affected infants do not survive beyond the first week of life. More than 10 children have survived to teenage years, but usually with marked handicaps.
Complications: Complications depend on the specific abnormalities that affect the infant.
Calling your health care provider: Call your health care provider and genetic counselor if you have had a child with Trisomy 18 and you plan to have another child.
Prevention: Prenatal diagnosis of trisomy 18 is possible with an amniocentesis and chromosome studies on amniotic cells. Parents who have a child with translocational trisomy 18 and want additional children should have chromosome studies, because they are at increased risk to have another child with trisomy 18.
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