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 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.
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 having Down syndrome. The American College of Obstetricians and Gynecologists (ACOG) has recommended that all pregnant women be offered DS screening tests.
Prenatal screening tests
- First 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 of pregnancy
- Second 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 of pregnancy
- Sequential and integrated maternal serum screening – combined first and second trimester screening test for open neural tube defects (ONTD), DS, and trisomy 18 (T18). Tests performed at the times noted in the two bullets above.
- Cell-free fetal DNA analysis – analyzes fetal DNA circulating in the mother's blood; the test is usually recommended at 10 weeks for women who are considered at a higher risk for having a baby with 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 is associated with these diagnostic tests. A sample may be obtained using one of the following techniques and chromosomal analysis (karyotype) is performed on the genetic material:
- Chorionic villus sampling (CVS) – 9th to 11th week of pregnancy
- Amniotic fluid analysis (amniocentesis) – 14th to 18th week of pregnancy
- Percutaneous umbilical blood sampling (PUBS) – 18th to 22nd week of pregnancy
- Chromosomal microarray testing – also uses samples collected via CVS or amniocentesis to examine the DNA of the unborn fetus for abnormalities
Diagnosis after birth
A diagnosis after birth is usually based initially on physical signs and characteristics. However, these signs and symptoms may also be seen in babies without Down syndrome. Diagnostic testing performed after birth involves taking a sample of blood from the baby and evaluating his or her chromosomes:
- 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.
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. A variety of laboratory tests may be used to detect conditions in an individual with Down syndrome as they arise. Some examples of these tests include:
- TSH and/or T4 – to detect thyroid disease, especially hypothyroidism. This condition may develop at any age for a person with Down syndrome, so screening is usually done as a newborn and then at regular intervals throughout the person's life.
- Complete blood count (CBC) – to detect anemia or infections and sometimes leukemia
- Glucose – to identify diabetes
- Celiac disease antibody tests – these tests may be recommended for children with Down syndrome as young as 2 years old or younger if they have signs and symptoms of the condition.
- 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. It may be performed as part of the first trimester pregnancy screen.
- Second trimester 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