Down Syndrome Information and Support

How is Down Syndrome Diagnosed?

There are two categories of tests available to detect Down syndrome that can be performed before a baby is born: screening tests and diagnostic tests. Screening tests estimate the chances of the fetus having Down syndrome. These tests do not tell you for sure whether your fetus has Down syndrome; they only provide a probability. Diagnostic tests can provide a definitive diagnosis with almost 100% accuracy.

The screening tests available for pregnant women involve a blood test and an ultrasound. The blood tests (eg. NIPT, Quad-Screen) measure quantities of various substances in the blood of the mother. Together with a woman’s age, are used to estimate her chance of having a child with Down syndrome. These blood tests are often performed in conjunction with a detailed ultrasound to check for “markers” such as extra fluid behind the baby’s neck.

The diagnostic procedures available for prenatal diagnosis of Down syndrome are chorionic villus sampling (CVS) and amniocentesis. These procedures, which carry up to a 1% risk of causing spontaneous termination (miscarriage), are nearly 100% accurate in diagnosing Down syndrome. Chorionic villus sampling (CVS) is performed in the first trimester between 9 and 14 weeks gestation whereas Amniocentesis is usually performed in the second trimester between 15 and 20 weeks.

Understanding a Diagnosis of Down Syndrome

What are the Different Types of Down Syndrome?

Trisomy 21: About 95% of people with Down syndrome have Trisomy 21. With this type of Down syndrome, each cell in the body has 3 separate copies of chromosome 21 instead of the usual 2 copies.

Mosaic Down Syndrome: This type affects about 2% of the people with Down syndrome. Mosaic means mixture or combination. For children with mosaic Down syndrome, some of their cells have 3 copies of chromosome 21, but other cells have the typical two copies of chromosome 21. Children with mosaic Down syndrome may have the same features as other children with Down Syndrome. However, they may have fewer features of the condition due to the presence of some (or many) cells with a typical number of chromosomes.

Translocation Down Syndrome: In translocation, which accounts for about 3% of cases of Down Syndrome, an extra copy of chromosome 21 is attached to a different chromosome rather than being a separate chromosome 21.

Some Common Physical Features of Babies with Down Syndrome

• Low muscle tone
• Loose joints
• Flat facial profile
• Small nose
• Upward slant to the eyes
• Small skin folds on the inner corner of the eyes
• Short neck
• Single, deep crease across the center of the palm
• Gap between the big toe and the rest of the toes
• Shorter in height as children and adults

Not all babies with Down syndrome have all these characteristics, and many of these features can be found to some extent, in individuals who do not have the condition. Even though people with Down syndrome might act and look similar, each person has differences in abilities. People with Down syndrome usually have an IQ in the mildly-to-moderately low range and are slower to speak than other children.

How Common is Down Syndrome?

Down syndrome remains the most common chromosomal condition diagnosed in the United States. Each year, about 6,000 babies born in the United States have Down syndrome. This means that Down syndrome occurs in about 1 out of every 700 babies. In Utah, an average of 77 pregnancies are affected by Down syndrome each year. This means that Down syndrome occurs in about 1 out of every 704 babies in Utah.

What Impact Does Down Syndrome Have on Society?

Individuals with Down syndrome are becoming increasingly integrated into society and community organizations, such as school, health care systems, work forces, and social and recreational activities. Individuals with Down syndrome possess varying degrees of cognitive delays, from very mild to severe. Most people with Down syndrome have cognitive delays that are mild to moderate.