Down Syndrome

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Tests

The goals of testing are to screen for Down syndrome during pregnancy, diagnose it in a fetus or newborn, detect any malformations or complications that will require medical interventions shortly after birth, and to monitor the person who has Down syndrome for complications throughout his or her life. Testing is usually a combination of laboratory and non-laboratory evaluations.

Laboratory Tests
Screening and diagnostic tests may be done during a woman's pregnancy, in either the first or the second trimester. Screening tests are not diagnostic; they indicate an increased likelihood of the fetus carrying Down syndrome. The American College of Obstetricians and Gynecologists (ACOG) has recommended that all pregnant women be offered DS screening tests.

Prenatal diagnostic tests may be performed when screening tests are abnormal. They involve taking samples of the fluid or tissues surrounding the baby and evaluating them for an additional copy or portion of chromosome 21. A very small risk of infection and miscarriage are associated with these diagnostic tests.

Diagnostic testing performed after birth involves taking a sample of blood from the baby and evaluating his or her chromosomes. Tests that detect the complications often seen in those with Down syndrome are used to help diagnose conditions that arise and to monitor the effectiveness of treatment. Some of the complications, such as congenital heart defects and gastrointestinal obstructions, may be present at birth. Others, such as hearing loss, vision disorders, leukemia, and thyroid disease, may develop at any time during the person's life.

Testing includes:

Prenatal screening

  • 1st trimester screen – nuchal translucency (non-laboratory test, see below), pregnancy-associated plasma protein A (PAPP-A), and free beta or total hCG (human chorionic gonadotropin), usually performed between 10 weeks, 4 days and 13 weeks, 6 days gestation
  • 2nd trimester screen (triple/quad screen) – alpha feto-protein (AFP), chorionic gonadotropin (hCG), and unconjugated estriol (uE3); quad screen adds inhibin A test; performed at 15 to 20 weeks gestation

Prenatal diagnosis

Diagnosis after birth

  • Chromosomal karyotype – cells are grown from a blood sample and chromosomes are evaluated for an extra copy of chromosome 21; the presence and type of Down syndrome can be determined from this test.

Non-Laboratory Tests

Prenatal

  • Nuchal translucency – an ultrasound measurement of the space between the fetal spine and the skin at the back of the neck; not diagnostic, but in a fetus with Down syndrome, there may be an increased amount of space. This test requires a person with specialized training to perform and interpret.
  • 2nd semester high-resolution ultrasound – can help monitor fetal development and detect malformations, such as cardiac and gastrointestinal defects

At or soon after birth

  • Echocardiogram and chest x-rays (to help detect cardiac defects)
  • Ultrasound and/or MRI (magnetic resonance imaging) to evaluate any suspected congenital conditions, such as cardiac defects and gastrointestinal obstructions
  • Hearing evaluation

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