Trisomy 18 is a genetic condition related to the presence of an
extra chromosome 18 caused by a problem that occurs when cells divide in the
egg, sperm, or fertilized egg. The extra chromosome causes the fetus to develop
abnormally with a number of physical and mental problems.
18 is also called Edward's syndrome. It is the second most common trisomy
condition. (Down syndrome is the most common.) A fetus with trisomy 18 has
three copies of chromosome 18 in each cell.
Trisomy 18 can be identified during
pregnancy. Doctors can do prenatal tests and fetal ultrasounds to screen for
problems, and they can do chromosome tests to diagnose trisomy 18.
Many fetuses with trisomy 18 do not survive to birth, but some are born
and live a couple of months to a couple of years. Babies born with trisomy 18
can have heart and kidney problems, a small
head with low-set ears, a chest with an unusual shape, and crossed legs. They
also have severe intellectual disability.