Down Syndrome Screening

Down Syndrome Screening

At the start of 11 weeks of pregnancy, you can choose to get screening for Down Syndrome.

These tests do not tell you if you have a baby with Down syndrome, but they tell you that you are at risk of having one.

Additional diagnostic tests are needed to determine if your baby will have down Syndrome.

What is Down Syndrome?

In humans, there are a total of 23 pairs of chromosomes in each of our cells. People with Down Syndrome, however, are born with an extra copy of chromosome 21.

Because of this third copy, this condition is also often referred to as Trisomy 21.  This abnormality in the number of chromosomes is the most common cause of:

  • significant mental retardation
  • delayed learning ability in children

Children born with this condition are also likely to develop heart, hearing and visual defects at birth or as they age. With the help of stimulation programs and proper health care, people with Down Syndrome can lead a healthy life and live up to 45-50 years old.​

Though it happens randomly, can occur at any age, and is rarely passed on from the parent’s genes, the risk becomes significantly higher in older mothers.

About 1 in 1,000 babies is born with Down’s syndrome.

How Do I know if my baby has Down Syndrome?

  1.  Screening Tests

In the past, tests for Down Syndrome were only typically offered to women aging 35 and above since the risk of having a baby with Down Syndrome increases with age.

With the advancement of technology, there are now improved non-invasive screening tests which are offered to all mothers irrespective of their age.

These screening tests can only be used to determine the chance of your baby having Down’s syndrome. Being non-invasive in nature, these screening tests does not have the risk for miscarriage. These screening tests include:

  • First trimester screening (FTS)

This screening involves a detailed ultrasound examination of the fetus at about 11–14 weeks of development to measure the nuchal translucency (NT) (the skin at the back of your baby’s neck).

Depending on the levels of thickness of the fluid-filled area, the risk of having Down Syndrome can be determined.

The accuracy of this test is about 75-80% and can increase up to 85% when combined with mother’s blood test results.

  • Maternal serum screening (MSS)

This screening involves measuring certain hormones called alpha-fetoprotein, human chorionic gonadotropin, with or without oestriol in the mother’s blood to determine risks.

Blood sample is taken at between 15-20 weeks of development, and a risk value is calculated in relation to the mother’s age. You are considered as screen positive if the screening test shows that the risk of Down syndrome is higher than 1 in 300.

 

  • Non-invasive prenatal testing (NIPT)

This screening involves a single blood test and can be done as early as 10 weeks of development. In this procedure, the mother’s blood examined for fragments of the baby’s DNA to determine the chance of having Down syndrome. This screening test can have detection rates as high as 99%. These tests are usually offered by private and specialized clinics.

Important note: Being screen positive does not automatically mean that your baby has Down syndrome. It just means that there is a higher risk and you may want to consider doing further diagnostic test to confirm the condition.

If you are screen negative, you may not opt to try confirmatory diagnostic tests since the chance of your baby to have Down Syndrome is low. However, these screening tests cannot assure that the baby will be 100% healthy as some issues can still be undetected or manifest later on.

  1. Diagnostic tests

These diagnostic tests are also called confirmatory test and are only offered to women with positive screening for Down Syndrome. While these tests can usually give you a sure answer, carrying out these tests increases the risk of causing a miscarriage. These diagnostic tests include:

 

  • Amniocentesis

This test is carried out by taking a sample of amniotic fluid surrounding the fetus at 15-20 weeks of development with the use of very fine needle being passed into the womb with the guidance of ultrasound imaging.

 

  • Chorionic villous sampling

This test is carried out by taking out placenta samples at 10-13 weeks of development for biopsy.  Like amniocentesis, the procedure is performed with the use of very fine needle being passed through the abdomen and the cervix with the guidance of ultrasound.

 

  • Fetal blood sampling

This test is carried out by taking sample of fetal blood from the umbilical cord. Compared to other diagnostic tests, the risk of miscarriage is significantly higher with this procedure.  Therefore, it is least recommended  for the diagnosis of Down Syndrome.

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