Down Syndrome Diagnosis
Tests used to diagnose Down syndrome include amniocentesis, chorionic villus sampling (CVS), and percutaneous umbilical blood sampling (PUBS). To confirm the diagnosis, the doctor may request a blood test called a chromosomal karyotype. The doctor may also diagnose the condition shortly after birth, based on the presence of possible characteristics of the disorder.
A Down syndrome diagnosis can be made during prenatal testing. A diagnosis can also be made shortly after birth. In this case, the doctor may suspect that a baby has Down syndrome based on the presence of possible characteristics of the condition. A diagnosis of Down syndrome is confirmed with a special blood test.
Prenatal screening for Down syndrome is available. This blood test goes by several names, including:
- Multiple marker screening test
- Maternal blood screening test
- Triple screen
- Quad screen.
This screening test suggests an increased likelihood of Down syndrome; it is not used to make a Down syndrome diagnosis.
(Click Prenatal Screening for Down Syndrome for more information about prenatal testing for the condition.)
Tests used to make a diagnosis include:
- Chorionic villus sampling (CVS)
- Percutaneous umbilical blood sampling (PUBS).
In amniocentesis, a sample of the fluid surrounding the fetus is withdrawn. Fetal cells in the fluid are then examined for chromosomal abnormalities. CVS is similar to amniocentesis, except that the procedure is done in the first trimester, and the fetal cells needed for examination are taken from the placenta. Neither procedure is used routinely, except when there is a family history of genetic defects, the pregnant woman is older than 35, or other medical indications are present.
Percutaneous umbilical blood sampling is the most accurate method used to confirm the results of CVS or amniocentesis. In PUBS, the tissue is tested for the presence of extra material from chromosome 21. PUBS cannot be done until a woman is 18 to 22 weeks pregnant.