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How is Down Syndrome Diagnosed?

Some of the Tests Commonly Used to Diagnose Down Syndrome

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Updated July 07, 2014

How is Down Syndrome Diagnosed?

Karyotype of Trisomy 21

K. Fergus

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.

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