Down syndrome

Tests

The goal of testing is to screen for Down syndrome, diagnose it, detect any malformations 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.

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, leukaemia, and thyroid disease may develop at any time during the patient’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 and 13 weeks gestation
2nd trimester screen - alpha feto-protein (AFP), chorionic gonadotropin (hCG), and unconjugated oestriol (uE3); quad screen adds inhibin A test; performed at 15 to 20 weeks gestation (see Maternal screening)

Prenatal diagnosis

Chorionic villi sampling (CVS) - 9th to 11th week of pregnancy
Amniocentesis - 14th to 18th week of pregnancy
Percutaneous umbilical blood sampling (PUBS) - 18th to 22nd week of pregnancy

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 specialised 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