Trisomy 18
(Edwards Syndrome)

Trisomy 18 Summary
Trisomy 18 is an chromosomal condition that causes severe birth defects in newborns. Many babies born with trisomy 18 do not live past one month of age. Trisomy 18 is also known as Edwards Syndrome.
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Trisomy 18 facts

  • Trisomy 18 (Edwards syndrome) results from the presence of an extra copy of chromosome 18.
  • Trisomy 18 leads to severe intellectual and physical defects.
  • The prognosis of trisomy 18 is poor; half of those affected do not live beyond the first week of life and only 10% of infants with this condition live beyond the first year.
  • Common features of trisomy 18 include a low birth weight; a small jaw and mouth; an abnormally shaped, small head; overlapping fingers and clenched fists; and defects in the heart and other organs.
  • Trisomy 18 occurs on average in 1 out of every 6,000 births.
  • Up to 95% of fetuses with trisomy 18 die in the prenatal period (prior to delivery).
  • Girls are affected more commonly than boys.

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Definition of Edwards Syndrome

Edwards syndrome: Trisomy 18 syndrome. Children with the syndrome have an extra chromosome 18 with a characteristic pattern of multiple malformations and mental retardation. Features include low birth weight, small head (microcephaly), small jaw (micrognathia), malformations of the heart and kidneys, clenched fists with abnormal finger positioning, and malformed feet. The mental retardation is profound with an IQ too low to measure. Nineteen out of 20 of these children die before their first birthday. The condition is named after the British physician and geneticist John Edwards who discovered the extra chromosome in 1960.