Diagnosis of Down syndrome

Updated at: Jan 22, 2013
Diagnosis of Down syndrome

Down’s syndrome can be detected by certain tests. If antenatal screening or ultrasound scan indicate that the baby is likely to have Down’s syndrome, further tests such as chorionic villus sampling (CVS) or amniocentesis are done. Afte

Dr Poonam Sachdev
Other DiseasesWritten by: Dr Poonam SachdevPublished at: May 30, 2012

Having a child with Down’s syndrome presents many challenges. Down’s syndrome can be detected by certain tests. Some types of screening tests are done in all pregnant women where as there are certain other tests that are done in women at high risk of having a child with Down’s syndrome.  

Antenatal screening

According to experts, all pregnant women, no matter what their age, should be advised to have screening for genetic conditions such as Down’s syndrome. Antenatal screening tests help to assess whether your foetus (unborn baby) has developed an abnormality during your pregnancy.

Screening can help to identify if the baby is likely to have Down’s syndrome. But screening tests are not 100% accurate. Even if the test is negative, there is a risk that the baby might have Down’s syndrome. Screening for Down’s syndrome is recommended in all women during pregnancy in order to identify women who are at high risk of giving birth to a child with Down’s syndrome.

If antenatal screening indicates that your baby is at risk of Down’s syndrome (or any other condition), further testing can be done to confirm whether or not your baby has the condition. Screening test for Down’s syndrome includes blood test and an ultrasound scan, known as the ‘combined test.’

Blood test: In this test, a sample of the mother’s blood is tested to check for levels of certain proteins and hormones. If the level of these substances is high in your blood, you may be at an increased risk of having a baby with Down’s syndrome.

Nuchal translucency: Ultrasound scans are done in pregnancy to check the development of your baby. It is a painless and non-invasive test that uses high-frequency sound waves to produce a picture of the inside of your body. A trained doctor can look at the images that are formed and detect normal and abnormal structures (in this case, your womb). In order to screen for Down’s syndrome, the doctor will look for nuchal translucency (fluid collected behind neck) during ultrasound scan.

To measure nuchal translucency, the doctor focuses on measuring the space between the spine and the nape (the back of the baby’s neck). All babies tend to collect fluid behind the neck, but the amount of fluid in babies with Down’s syndrome tends to be more. Measuring the thickness of this fluid is useful to determine if your baby is likely to have Down’s syndrome.

Diagnostic tests

If antenatal screening test indicate that the baby is likely to have Down’s syndrome, you may be advised to have further tests. Diagnostic tests which can diagnose Down’s syndrome while your baby is still in the womb are:

  • Chorionic villus sampling (CVS) a small sample of the placenta is taken for testing to diagnose if the baby has Down’s syndrome.
  • Amniocentesis A small sample of amniotic fluid (the fluid that surrounds the foetus in the womb) is taken for testing to diagnose if the baby has Down’s syndrome.

Diagnosis after birth

After the baby is born, Down’s syndrome is suspected based on your baby’s physical appearance such as eyes that slant upwards or a flat back of the head. To confirm the diagnosis, the blood test known as a chromosomal karyotype is done. In this test a sample of your baby’s blood is tested so that the chromosomes in the blood can be analysed. If an extra chromosome 21 is detected, your baby will be diagnosed with Down’s syndrome.


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