How is Down syndrome diagnosed?
Down syndrome is usually identified at birth or shortly thereafter. Initially the diagnosis is based on physical characteristics that are commonly seen in babies with Down syndrome, which include low muscle tone, a single crease across the palm of the hand, a slightly flattened facial profile and an upward slant to the eyes. The diagnosis must be confirmed by a chromosome study (karyotype) that will provide a visual display of the chromosomes grouped by their size, number and shape. This chromosome study may be performed by examining blood or tissue cells and is not related to race, nationality, religion or socioeconomic status of the individual.
What pre-natal screenings are available for expecting families?
Two types of procedures are available to pregnant women: screening tests and diagnostic tests. The screening tests estimate the risk of the baby having Down syndrome while diagnostic tests tell whether or not the baby actually has Down syndrome.
At this time the most commonly used screening test is “The Triple Screen.” This is a combination of three tests that measure quantities of various substances in the blood. These tests are usually done between 15 and 20 weeks of gestation. Sonograms (ultrasounds) are usually performed in conjunction with other screenings. These can show some physical traits that are helpful in calculating the risk of Down syndrome. Screening tests do not accurately confirm the diagnosis of Down syndrome. In fact, false positives and false negatives frequently occur.
Diagnostic procedures for the prenatal diagnosis of Down syndrome include chorionic villus sampling (CVS) and amniocentesis. Both procedures are invasive and carry up to a 1% risk of miscarriage; however they are almost 100% accurate. CVS is generally performed in the first trimester between 9 and 11 weeks; amniocentesis after 15 weeks gestation.