Trisomy 18 is a genetic disorder in which a person has a third
copy of material from chromosome 18, instead of the usual two
copies. Trisomy 18 is a somewhat common syndrome. It is three
times more common in girls than boys. The syndrome occurs when
there is extra material from chromosome 18. The extra material
affects normal development. Exams and Tests An exam during
pregnancy may show an unusually large uterus and extra amniotic
fluid. There may be an unusually small placenta when the baby is
born. A physical exam of the infant may show unusual fingerprint
patterns. X-rays may show a short breast bone. Chromosome
studies will show trisomy 18, partial trisomy, or translocation.
Other signs include: There are often signs of congenital heart
disease, such as: Tests may also show kidney problems,
including: Treatment of children with trisomy 18 is planned on a
case-by-case basis. Which treatments are used depend on the
patient's individual condition. Half of infants with this
condition do not survive beyond th