What is Trisomy 13?

Trisomy 13 syndrome is a rare chromosomal disorder in which all or a large portion of chromosome 13 is present three times (trisomy), rather than twice in each cell of the body. This extra copy changes how the baby's body and brain develop, which can cause distinctive physical features, structural birth defects and developmental disabilities.  Chromosome abnormalities are usually present at conception, the result of errors in egg or sperm formation. In rare cases chromosome abnormalities are inherited. The majority of babies born with trisomy 13 are female. Trisomy 13 can be diagnosed prenatally by amniocentesis or chorionic villus sampling.

One factor that increases the risk for having a baby with trisomy 13 is the mother's age. Women who are 35 years or older when they become pregnant are more likely to have a pregnancy affected by trisomy 13 than women who become pregnant at a younger age.