Down Syndrome Tests

Down syndrome tests are medical procedures used to detect the presence of Down syndrome in a fetus or newborn. Down syndrome is a genetic disorder caused by an extra copy of chromosome 21, which can lead to intellectual disability, delayed speech, and physical characteristics such as a flat face and short neck.

Types of Tests

• Screening tests: These tests measure the risk of Down syndrome in a fetus. They include:
  • Nuchal translucency (NT) scan: measures the thickness of the fluid-filled space at the back of the fetus's neck
  • Maternal serum screening: measures the levels of certain substances in the mother's blood, such as alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3)
  • Cell-free DNA testing: analyzes the DNA present in the mother's bloodstream to detect the presence of an extra copy of chromosome 21
• Diagnostic tests: These tests can confirm the presence of Down syndrome. They include:
  • Chorionic villus sampling (CVS): involves removing a sample of cells from the placenta and analyzing them for chromosomal abnormalities
  • Amniocentesis: involves removing a sample of amniotic fluid and analyzing the cells present in it for chromosomal abnormalities
  • Percutaneous umbilical blood sampling (PUBS): involves removing a sample of blood from the umbilical cord and analyzing it for chromosomal abnormalities

Risk Factors

Certain factors can increase the risk of having a child with Down syndrome, including:

• Advanced maternal age: women over 35 years old are at higher risk
• Family history: having a previous child with Down syndrome or a family history of chromosomal abnormalities
• Carrying a balanced translocation: some people may carry a balanced translocation, which can increase the risk of having a child with Down syndrome

Interpretation of Results

The results of Down syndrome tests are usually presented as a probability or risk. A positive result does not necessarily mean that the fetus has Down syndrome, but rather that there is an increased risk. A negative result does not guarantee that the fetus does not have Down syndrome, but rather that the risk is lower.

Follow-up Testing

If a screening test indicates an increased risk of Down syndrome, follow-up testing may be recommended to confirm the diagnosis. This can include diagnostic tests such as CVS or amniocentesis.

Counseling and Support

Receiving a diagnosis of Down syndrome can be a challenging experience for families. Genetic counseling and support services are available to provide information, guidance, and emotional support throughout the testing process and beyond.