Most cases of Trisomy 18 are diagnosed prenatally in the United States. Regardless of whether the diagnosis is made prenatally or postnatally (after birth) the process is the same. A sample of the baby’s dna is extracted from a blood sample or other bodily cells or tissue and is cultured to examine a picture of the chromosomes called a karyotype. A karyotype is simply a picture of a person’s chromosomes. In order to get this picture, the chromosomes are isolated, stained, and examined under the microscope. Most often, this is done using the chromosomes in the white blood cells. A picture of the chromosomes is taken through the microscope. A visible extra 18th chromosome confirms a Trisomy 18 diagnosis.
