How is Down Syndrome Diagnosed?

How is Down's Syndrome Diagnosed?

Down syndrome is diagnosed one of two ways, either during pregnancy or shortly after birth. The diagnosis is always based on the presence of an extra number 21 chromosome on a karyotype (a picture of an individual's chromosomes).

At Birth

The diagnosis of Down's syndrome is usually made soon after birth because of some subtle differences in the baby's appearance. Children with Down syndrome have some distinctive facial features and physical characteristics that may lead your doctor to suspect that your baby has Down syndrome.

Some of the features include:

• A flat facial profile, flat nasal bridge and somewhat small nose
• Almond shaped eyes with epicanthal folds
• A small mouth with a slightly enlarged tongue
• A big space between the first and second toe
• Small broad hands with short fingers and a little finger that curves inwards.
• A single palmar crease on their hand
• Reduced muscle tone (hypotonia) which results in floppiness

If the doctor suspects that the baby has Down syndrome, a chromosome test called a karyotype, will be ordered. It usually takes a few days to get the results of this blood test. It is almost always a shock when a baby is diagnosed with Down syndrome but there are some things that you can do to get through the first few months.

During pregnancy

Screening versus Diagnostic Testing

There are two kinds of testing that can be done during a pregnancy - diagnostic testing such as amniocentesis and chorionic villi sampling (CVS), and screening testing such as ultrasound (sonogram) and maternal serum screening tests. A screening test can never give you a firm diagnosis - a screening tests simply tells you if you have a slightly higher risk to have a baby with Down syndrome. A diagnostic test on other hand, gives you a firm diagnosis.

Down syndrome can be diagnosed in pregnancy by diagnostic tests such as amniocentesis or chorionic villi sampling (CVS). These are considered optional tests during pregnancy which means that it is your choice whether or not to have this testing. It is recommended that women considering testing speak with a genetic counselor to review their risks and to discuss risks and benefits of these procedures before making their decision about testing

The results of amniocentesis and CVS will give you a picture of the fetus’s chromosomes and the diagnosis of Down syndrome is very straightforward. Infants with Down syndrome have an extra number 21 chromosome for a total of 47 chromosomes rather than 46.